This part of the reference documentation is concerned with data access and the
interaction between the data access layer and the business or service layer.

Spring’s comprehensive transaction management support is covered in some detail,
followed by thorough coverage of the various data access frameworks and technologies
that the Spring Framework integrates with.

1. Transaction Management

1.1. Introduction to Spring Framework transaction management

Comprehensive transaction support is among the most compelling reasons to use the Spring
Framework. The Spring Framework provides a consistent abstraction for transaction
management that delivers the following benefits:

Simpler API for programmatic transaction management than
complex transaction APIs such as JTA.

Excellent integration with Spring’s data access abstractions.

The following sections describe the Spring Framework’s transaction value-adds and
technologies. (The chapter also includes discussions of best practices, application
server integration, and solutions to common problems.)

1.2. Advantages of the Spring Framework’s transaction support model

Traditionally, Java EE developers have had two choices for transaction management:
global or local transactions, both of which have profound limitations. Global
and local transaction management is reviewed in the next two sections, followed by a
discussion of how the Spring Framework’s transaction management support addresses the
limitations of the global and local transaction models.

1.2.1. Global transactions

Global transactions enable you to work with multiple transactional resources, typically
relational databases and message queues. The application server manages global
transactions through the JTA, which is a cumbersome API to use (partly due to its
exception model). Furthermore, a JTA UserTransaction normally needs to be sourced from
JNDI, meaning that you also need to use JNDI in order to use JTA. Obviously the use
of global transactions would limit any potential reuse of application code, as JTA is
normally only available in an application server environment.

Previously, the preferred way to use global transactions was via EJB CMT
(Container Managed Transaction): CMT is a form of declarative transaction
management (as distinguished from programmatic transaction management). EJB CMT
removes the need for transaction-related JNDI lookups, although of course the use of EJB
itself necessitates the use of JNDI. It removes most but not all of the need to write
Java code to control transactions. The significant downside is that CMT is tied to JTA
and an application server environment. Also, it is only available if one chooses to
implement business logic in EJBs, or at least behind a transactional EJB facade. The
negatives of EJB in general are so great that this is not an attractive proposition,
especially in the face of compelling alternatives for declarative transaction management.

1.2.2. Local transactions

Local transactions are resource-specific, such as a transaction associated with a JDBC
connection. Local transactions may be easier to use, but have significant disadvantages:
they cannot work across multiple transactional resources. For example, code that manages
transactions using a JDBC connection cannot run within a global JTA transaction. Because
the application server is not involved in transaction management, it cannot help ensure
correctness across multiple resources. (It is worth noting that most applications use a
single transaction resource.) Another downside is that local transactions are invasive
to the programming model.

1.2.3. Spring Framework’s consistent programming model

Spring resolves the disadvantages of global and local transactions. It enables
application developers to use a consistent programming model in any environment.
You write your code once, and it can benefit from different transaction management
strategies in different environments. The Spring Framework provides both declarative and
programmatic transaction management. Most users prefer declarative transaction
management, which is recommended in most cases.

With programmatic transaction management, developers work with the Spring Framework
transaction abstraction, which can run over any underlying transaction infrastructure.
With the preferred declarative model, developers typically write little or no code
related to transaction management, and hence do not depend on the Spring Framework
transaction API, or any other transaction API.

Do you need an application server for transaction management?

The Spring Framework’s transaction management support changes traditional rules as to
when an enterprise Java application requires an application server.

In particular, you do not need an application server simply for declarative transactions
through EJBs. In fact, even if your application server has powerful JTA capabilities,
you may decide that the Spring Framework’s declarative transactions offer more power and
a more productive programming model than EJB CMT.

Typically you need an application server’s JTA capability only if your application needs
to handle transactions across multiple resources, which is not a requirement for many
applications. Many high-end applications use a single, highly scalable database (such as
Oracle RAC) instead. Standalone transaction managers such as
Atomikos Transactions and JOTM
are other options. Of course, you may need other application server capabilities such as
Java Message Service (JMS) and Java EE Connector Architecture (JCA).

The Spring Framework gives you the choice of when to scale your application to a fully
loaded application server. Gone are the days when the only alternative to using EJB
CMT or JTA was to write code with local transactions such as those on JDBC connections,
and face a hefty rework if you need that code to run within global, container-managed
transactions. With the Spring Framework, only some of the bean definitions in your
configuration file, rather than your code, need to change.

1.3. Understanding the Spring Framework transaction abstraction

The key to the Spring transaction abstraction is the notion of a transaction
strategy. A transaction strategy is defined by the
org.springframework.transaction.PlatformTransactionManager interface:

This is primarily a service provider interface (SPI), although it can be used
programmatically from your application code. Because
PlatformTransactionManager is an interface, it can be easily mocked or stubbed as
necessary. It is not tied to a lookup strategy such as JNDI.
PlatformTransactionManager implementations are defined like any other object (or bean)
in the Spring Framework IoC container. This benefit alone makes Spring Framework
transactions a worthwhile abstraction even when you work with JTA. Transactional code
can be tested much more easily than if it used JTA directly.

Again in keeping with Spring’s philosophy, the TransactionException that can be thrown
by any of the PlatformTransactionManager interface’s methods is unchecked (that
is, it extends the java.lang.RuntimeException class). Transaction infrastructure
failures are almost invariably fatal. In rare cases where application code can actually
recover from a transaction failure, the application developer can still choose to catch
and handle TransactionException. The salient point is that developers are not
forced to do so.

The getTransaction(..) method returns a TransactionStatus object, depending on a
TransactionDefinition parameter. The returned TransactionStatus might represent a
new transaction, or can represent an existing transaction if a matching transaction
exists in the current call stack. The implication in this latter case is that, as with
Java EE transaction contexts, a TransactionStatus is associated with a thread of
execution.

The TransactionDefinition interface specifies:

Propagation: Typically, all code executed within a transaction scope will run in
that transaction. However, you have the option of specifying the behavior in the event
that a transactional method is executed when a transaction context already exists. For
example, code can continue running in the existing transaction (the common case); or
the existing transaction can be suspended and a new transaction created. Spring
offers all of the transaction propagation options familiar from EJB CMT. To read
about the semantics of transaction propagation in Spring, see Transaction propagation.

Isolation: The degree to which this transaction is isolated from the work of other
transactions. For example, can this transaction see uncommitted writes from other
transactions?

Timeout: How long this transaction runs before timing out and being rolled back
automatically by the underlying transaction infrastructure.

Read-only status: A read-only transaction can be used when your code reads but
does not modify data. Read-only transactions can be a useful optimization in some
cases, such as when you are using Hibernate.

These settings reflect standard transactional concepts. If necessary, refer to resources
that discuss transaction isolation levels and other core transaction concepts.
Understanding these concepts is essential to using the Spring Framework or any
transaction management solution.

The TransactionStatus interface provides a simple way for transactional code to
control transaction execution and query transaction status. The concepts should be
familiar, as they are common to all transaction APIs:

Regardless of whether you opt for declarative or programmatic transaction management in
Spring, defining the correct PlatformTransactionManager implementation is absolutely
essential. You typically define this implementation through dependency injection.

PlatformTransactionManager implementations normally require knowledge of the
environment in which they work: JDBC, JTA, Hibernate, and so on. The following examples
show how you can define a local PlatformTransactionManager implementation. (This
example works with plain JDBC.)

If you use JTA in a Java EE container then you use a container DataSource, obtained
through JNDI, in conjunction with Spring’s JtaTransactionManager. This is what the JTA
and JNDI lookup version would look like:

The JtaTransactionManager does not need to know about the DataSource, or any other
specific resources, because it uses the container’s global transaction management
infrastructure.

The above definition of the dataSource bean uses the <jndi-lookup/> tag from the
jee namespace. For more information see
The JEE schema.

You can also use Hibernate local transactions easily, as shown in the following
examples. In this case, you need to define a Hibernate LocalSessionFactoryBean, which
your application code will use to obtain Hibernate Session instances.

The DataSource bean definition will be similar to the local JDBC example shown
previously and thus is not shown in the following example.

If the DataSource, used by any non-JTA transaction manager, is looked up via JNDI and
managed by a Java EE container, then it should be non-transactional because the Spring
Framework, rather than the Java EE container, will manage the transactions.

The txManager bean in this case is of the HibernateTransactionManager type. In the
same way as the DataSourceTransactionManager needs a reference to the DataSource,
the HibernateTransactionManager needs a reference to the SessionFactory.

If you use JTA , then your transaction manager definition will look the same regardless
of what data access technology you use, be it JDBC, Hibernate JPA or any other supported
technology. This is due to the fact that JTA transactions are global transactions, which
can enlist any transactional resource.

In all these cases, application code does not need to change. You can change how
transactions are managed merely by changing configuration, even if that change means
moving from local to global transactions or vice versa.

1.4. Synchronizing resources with transactions

It should now be clear how you create different transaction managers, and how they are
linked to related resources that need to be synchronized to transactions (for example
DataSourceTransactionManager to a JDBC DataSource, HibernateTransactionManager to
a Hibernate SessionFactory, and so forth). This section describes how the application
code, directly or indirectly using a persistence API such as JDBC, Hibernate, or JPA,
ensures that these resources are created, reused, and cleaned up properly. The section
also discusses how transaction synchronization is triggered (optionally) through the
relevant PlatformTransactionManager.

1.4.1. High-level synchronization approach

The preferred approach is to use Spring’s highest level template based persistence
integration APIs or to use native ORM APIs with transaction- aware factory beans or
proxies for managing the native resource factories. These transaction-aware solutions
internally handle resource creation and reuse, cleanup, optional transaction
synchronization of the resources, and exception mapping. Thus user data access code does
not have to address these tasks, but can be focused purely on non-boilerplate
persistence logic. Generally, you use the native ORM API or take a template approach
for JDBC access by using the JdbcTemplate. These solutions are detailed in subsequent
chapters of this reference documentation.

1.4.2. Low-level synchronization approach

Classes such as DataSourceUtils (for JDBC), EntityManagerFactoryUtils (for JPA),
SessionFactoryUtils (for Hibernate), and so on exist at a lower level. When you want the
application code to deal directly with the resource types of the native persistence APIs,
you use these classes to ensure that proper Spring Framework-managed instances are obtained,
transactions are (optionally) synchronized, and exceptions that occur in the process are
properly mapped to a consistent API.

For example, in the case of JDBC, instead of the traditional JDBC approach of calling
the getConnection() method on the DataSource, you instead use Spring’s
org.springframework.jdbc.datasource.DataSourceUtils class as follows:

Connection conn = DataSourceUtils.getConnection(dataSource);

If an existing transaction already has a connection synchronized (linked) to it, that
instance is returned. Otherwise, the method call triggers the creation of a new
connection, which is (optionally) synchronized to any existing transaction, and made
available for subsequent reuse in that same transaction. As mentioned, any
SQLException is wrapped in a Spring Framework CannotGetJdbcConnectionException, one
of the Spring Framework’s hierarchy of unchecked DataAccessExceptions. This approach
gives you more information than can be obtained easily from the SQLException, and
ensures portability across databases, even across different persistence technologies.

This approach also works without Spring transaction management (transaction
synchronization is optional), so you can use it whether or not you are using Spring for
transaction management.

Of course, once you have used Spring’s JDBC support, JPA support or Hibernate support,
you will generally prefer not to use DataSourceUtils or the other helper classes,
because you will be much happier working through the Spring abstraction than directly
with the relevant APIs. For example, if you use the Spring JdbcTemplate or
jdbc.object package to simplify your use of JDBC, correct connection retrieval occurs
behind the scenes and you won’t need to write any special code.

1.4.3. TransactionAwareDataSourceProxy

At the very lowest level exists the TransactionAwareDataSourceProxy class. This is a
proxy for a target DataSource, which wraps the target DataSource to add awareness of
Spring-managed transactions. In this respect, it is similar to a transactional JNDI
DataSource as provided by a Java EE server.

It should almost never be necessary or desirable to use this class, except when existing
code must be called and passed a standard JDBC DataSource interface implementation. In
that case, it is possible that this code is usable, but participating in Spring managed
transactions. It is preferable to write your new code by using the higher level
abstractions mentioned above.

1.5. Declarative transaction management

Most Spring Framework users choose declarative transaction management. This option has
the least impact on application code, and hence is most consistent with the ideals of a
non-invasive lightweight container.

The Spring Framework’s declarative transaction management is made possible with Spring
aspect-oriented programming (AOP), although, as the transactional aspects code comes
with the Spring Framework distribution and may be used in a boilerplate fashion, AOP
concepts do not generally have to be understood to make effective use of this code.

The Spring Framework’s declarative transaction management is similar to EJB CMT in that
you can specify transaction behavior (or lack of it) down to individual method level. It
is possible to make a setRollbackOnly() call within a transaction context if
necessary. The differences between the two types of transaction management are:

Unlike EJB CMT, which is tied to JTA, the Spring Framework’s declarative transaction
management works in any environment. It can work with JTA transactions or local
transactions using JDBC, JPA or Hibernate by simply adjusting the configuration
files.

You can apply the Spring Framework declarative transaction management to any class,
not merely special classes such as EJBs.

The Spring Framework offers declarative
rollback rules, a feature with no EJB
equivalent. Both programmatic and declarative support for rollback rules is provided.

The Spring Framework enables you to customize transactional behavior, by using AOP.
For example, you can insert custom behavior in the case of transaction rollback. You
can also add arbitrary advice, along with the transactional advice. With EJB CMT, you
cannot influence the container’s transaction management except with
setRollbackOnly().

The Spring Framework does not support propagation of transaction contexts across
remote calls, as do high-end application servers. If you need this feature, we
recommend that you use EJB. However, consider carefully before using such a feature,
because normally, one does not want transactions to span remote calls.

Where is TransactionProxyFactoryBean?

Declarative transaction configuration in versions of Spring 2.0 and above differs
considerably from previous versions of Spring. The main difference is that there is no
longer any need to configure TransactionProxyFactoryBean beans.

The pre-Spring 2.0 configuration style is still 100% valid configuration; think of the
new <tx:tags/> as simply defining TransactionProxyFactoryBean beans on your behalf.

The concept of rollback rules is important: they enable you to specify which exceptions
(and throwables) should cause automatic rollback. You specify this declaratively, in
configuration, not in Java code. So, although you can still call setRollbackOnly() on
the TransactionStatus object to roll back the current transaction back, most often you
can specify a rule that MyApplicationException must always result in rollback. The
significant advantage to this option is that business objects do not depend on the
transaction infrastructure. For example, they typically do not need to import Spring
transaction APIs or other Spring APIs.

Although EJB container default behavior automatically rolls back the transaction on a
system exception (usually a runtime exception), EJB CMT does not roll back the
transaction automatically on anapplication exception (that is, a checked exception
other than java.rmi.RemoteException). While the Spring default behavior for
declarative transaction management follows EJB convention (roll back is automatic only
on unchecked exceptions), it is often useful to customize this behavior.

It is not sufficient to tell you simply to annotate your classes with the
@Transactional annotation, add @EnableTransactionManagement to your configuration,
and then expect you to understand how it all works. This section explains the inner
workings of the Spring Framework’s declarative transaction infrastructure in the event
of transaction-related issues.

The most important concepts to grasp with regard to the Spring Framework’s declarative
transaction support are that this support is enabled
via AOP proxies, and that the transactional advice
is driven by metadata (currently XML- or annotation-based). The combination of AOP
with transactional metadata yields an AOP proxy that uses a TransactionInterceptor in
conjunction with an appropriate PlatformTransactionManager implementation to drive
transactions around method invocations.

Conceptually, calling a method on a transactional proxy looks like this…​

1.5.2. Example of declarative transaction implementation

Consider the following interface, and its attendant implementation. This example uses
Foo and Bar classes as placeholders so that you can concentrate on the transaction
usage without focusing on a particular domain model. For the purposes of this example,
the fact that the DefaultFooService class throws UnsupportedOperationException
instances in the body of each implemented method is good; it allows you to see
transactions created and then rolled back in response to the
UnsupportedOperationException instance.

Assume that the first two methods of the FooService interface, getFoo(String) and
getFoo(String, String), must execute in the context of a transaction with read-only
semantics, and that the other methods, insertFoo(Foo) and updateFoo(Foo), must
execute in the context of a transaction with read-write semantics. The following
configuration is explained in detail in the next few paragraphs.

<!-- from the file 'context.xml' --><?xml version="1.0" encoding="UTF-8"?><beansxmlns="http://www.springframework.org/schema/beans"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xmlns:aop="http://www.springframework.org/schema/aop"xmlns:tx="http://www.springframework.org/schema/tx"xsi:schemaLocation="http://www.springframework.org/schema/beanshttp://www.springframework.org/schema/beans/spring-beans.xsdhttp://www.springframework.org/schema/txhttp://www.springframework.org/schema/tx/spring-tx.xsdhttp://www.springframework.org/schema/aophttp://www.springframework.org/schema/aop/spring-aop.xsd"><!-- this is the service object that we want to make transactional --><beanid="fooService"class="x.y.service.DefaultFooService"/><!-- the transactional advice (what 'happens'; see the <aop:advisor/> bean below) --><tx:adviceid="txAdvice"transaction-manager="txManager"><!-- the transactional semantics... --><tx:attributes><!-- all methods starting with 'get' are read-only --><tx:methodname="get*"read-only="true"/><!-- other methods use the default transaction settings (see below) --><tx:methodname="*"/></tx:attributes></tx:advice><!-- ensure that the above transactional advice runs for any execution
of an operation defined by the FooService interface --><aop:config><aop:pointcutid="fooServiceOperation"expression="execution(* x.y.service.FooService.*(..))"/><aop:advisoradvice-ref="txAdvice"pointcut-ref="fooServiceOperation"/></aop:config><!-- don't forget the DataSource --><beanid="dataSource"class="org.apache.commons.dbcp.BasicDataSource"destroy-method="close"><propertyname="driverClassName"value="oracle.jdbc.driver.OracleDriver"/><propertyname="url"value="jdbc:oracle:thin:@rj-t42:1521:elvis"/><propertyname="username"value="scott"/><propertyname="password"value="tiger"/></bean><!-- similarly, don't forget the PlatformTransactionManager --><beanid="txManager"class="org.springframework.jdbc.datasource.DataSourceTransactionManager"><propertyname="dataSource"ref="dataSource"/></bean><!-- other <bean/> definitions here --></beans>

Examine the preceding configuration. You want to make a service object, the fooService
bean, transactional. The transaction semantics to apply are encapsulated in the
<tx:advice/> definition. The <tx:advice/> definition reads as "…​ all methods on
starting with 'get' are to execute in the context of a read-only transaction, and all
other methods are to execute with the default transaction semantics". The
transaction-manager attribute of the <tx:advice/> tag is set to the name of the
PlatformTransactionManager bean that is going to drive the transactions, in this
case, the txManager bean.

You can omit the transaction-manager attribute in the transactional advice
(<tx:advice/>) if the bean name of the PlatformTransactionManager that you want to
wire in has the name transactionManager. If the PlatformTransactionManager bean that
you want to wire in has any other name, then you must use the transaction-manager
attribute explicitly, as in the preceding example.

The <aop:config/> definition ensures that the transactional advice defined by the
txAdvice bean executes at the appropriate points in the program. First you define a
pointcut that matches the execution of any operation defined in the FooService
interface ( fooServiceOperation). Then you associate the pointcut with the txAdvice
using an advisor. The result indicates that at the execution of a fooServiceOperation,
the advice defined by txAdvice will be run.

The expression defined within the <aop:pointcut/> element is an AspectJ pointcut
expression; see the AOP section for more details on pointcut expressions in Spring.

A common requirement is to make an entire service layer transactional. The best way to
do this is simply to change the pointcut expression to match any operation in your
service layer. For example:

In this example it is assumed that all your service interfaces are defined in the
x.y.service package; see the AOP section for more details.

Now that we’ve analyzed the configuration, you may be asking yourself, "Okay…​ but
what does all this configuration actually do?".

The above configuration will be used to create a transactional proxy around the object
that is created from the fooService bean definition. The proxy will be configured with
the transactional advice, so that when an appropriate method is invoked on the
proxy, a transaction is started, suspended, marked as read-only, and so on, depending
on the transaction configuration associated with that method. Consider the following
program that test drives the above configuration:

The output from running the preceding program will resemble the following. (The Log4J
output and the stack trace from the UnsupportedOperationException thrown by the
insertFoo(..) method of the DefaultFooService class have been truncated for clarity.)

1.5.3. Rolling back a declarative transaction

The previous section outlined the basics of how to specify transactional settings for
classes, typically service layer classes, declaratively in your application. This
section describes how you can control the rollback of transactions in a simple
declarative fashion.

The recommended way to indicate to the Spring Framework’s transaction infrastructure
that a transaction’s work is to be rolled back is to throw an Exception from code that
is currently executing in the context of a transaction. The Spring Framework’s
transaction infrastructure code will catch any unhandled Exception as it bubbles up
the call stack, and make a determination whether to mark the transaction for rollback.

In its default configuration, the Spring Framework’s transaction infrastructure code
only marks a transaction for rollback in the case of runtime, unchecked exceptions;
that is, when the thrown exception is an instance or subclass of RuntimeException. (
Errors will also - by default - result in a rollback). Checked exceptions that are
thrown from a transactional method do not result in rollback in the default
configuration.

You can configure exactly which Exception types mark a transaction for rollback,
including checked exceptions. The following XML snippet demonstrates how you configure
rollback for a checked, application-specific Exception type.

You can also specify 'no rollback rules', if you do not want a transaction rolled
back when an exception is thrown. The following example tells the Spring Framework’s
transaction infrastructure to commit the attendant transaction even in the face of an
unhandled InstrumentNotFoundException.

When the Spring Framework’s transaction infrastructure catches an exception and it
consults configured rollback rules to determine whether to mark the transaction for
rollback, the strongest matching rule wins. So in the case of the following
configuration, any exception other than an InstrumentNotFoundException results in a
rollback of the attendant transaction.

You are strongly encouraged to use the declarative approach to rollback if at all
possible. Programmatic rollback is available should you absolutely need it, but its
usage flies in the face of achieving a clean POJO-based architecture.

1.5.4. Configuring different transactional semantics for different beans

Consider the scenario where you have a number of service layer objects, and you want to
apply a totally different transactional configuration to each of them. You do this
by defining distinct <aop:advisor/> elements with differing pointcut and
advice-ref attribute values.

As a point of comparison, first assume that all of your service layer classes are
defined in a root x.y.service package. To make all beans that are instances of classes
defined in that package (or in subpackages) and that have names ending in Service have
the default transactional configuration, you would write the following:

<?xml version="1.0" encoding="UTF-8"?><beansxmlns="http://www.springframework.org/schema/beans"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xmlns:aop="http://www.springframework.org/schema/aop"xmlns:tx="http://www.springframework.org/schema/tx"xsi:schemaLocation="http://www.springframework.org/schema/beanshttp://www.springframework.org/schema/beans/spring-beans.xsdhttp://www.springframework.org/schema/txhttp://www.springframework.org/schema/tx/spring-tx.xsdhttp://www.springframework.org/schema/aophttp://www.springframework.org/schema/aop/spring-aop.xsd"><aop:config><aop:pointcutid="serviceOperation"expression="execution(* x.y.service..*Service.*(..))"/><aop:advisorpointcut-ref="serviceOperation"advice-ref="txAdvice"/></aop:config><!-- these two beans will be transactional... --><beanid="fooService"class="x.y.service.DefaultFooService"/><beanid="barService"class="x.y.service.extras.SimpleBarService"/><!-- ... and these two beans won't --><beanid="anotherService"class="org.xyz.SomeService"/><!-- (not in the right package) --><beanid="barManager"class="x.y.service.SimpleBarManager"/><!-- (doesn't end in 'Service') --><tx:adviceid="txAdvice"><tx:attributes><tx:methodname="get*"read-only="true"/><tx:methodname="*"/></tx:attributes></tx:advice><!-- other transaction infrastructure beans such as a PlatformTransactionManager omitted... --></beans>

The following example shows how to configure two distinct beans with totally different
transactional settings.

<?xml version="1.0" encoding="UTF-8"?><beansxmlns="http://www.springframework.org/schema/beans"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xmlns:aop="http://www.springframework.org/schema/aop"xmlns:tx="http://www.springframework.org/schema/tx"xsi:schemaLocation="http://www.springframework.org/schema/beanshttp://www.springframework.org/schema/beans/spring-beans.xsdhttp://www.springframework.org/schema/txhttp://www.springframework.org/schema/tx/spring-tx.xsdhttp://www.springframework.org/schema/aophttp://www.springframework.org/schema/aop/spring-aop.xsd"><aop:config><aop:pointcutid="defaultServiceOperation"expression="execution(* x.y.service.*Service.*(..))"/><aop:pointcutid="noTxServiceOperation"expression="execution(* x.y.service.ddl.DefaultDdlManager.*(..))"/><aop:advisorpointcut-ref="defaultServiceOperation"advice-ref="defaultTxAdvice"/><aop:advisorpointcut-ref="noTxServiceOperation"advice-ref="noTxAdvice"/></aop:config><!-- this bean will be transactional (see the 'defaultServiceOperation' pointcut) --><beanid="fooService"class="x.y.service.DefaultFooService"/><!-- this bean will also be transactional, but with totally different transactional settings --><beanid="anotherFooService"class="x.y.service.ddl.DefaultDdlManager"/><tx:adviceid="defaultTxAdvice"><tx:attributes><tx:methodname="get*"read-only="true"/><tx:methodname="*"/></tx:attributes></tx:advice><tx:adviceid="noTxAdvice"><tx:attributes><tx:methodname="*"propagation="NEVER"/></tx:attributes></tx:advice><!-- other transaction infrastructure beans such as a PlatformTransactionManager omitted... --></beans>

1.5.5. <tx:advice/> settings

This section summarizes the various transactional settings that can be specified using
the <tx:advice/> tag. The default <tx:advice/> settings are:

Transaction timeout defaults to the default timeout of the underlying transaction
system, or none if timeouts are not supported.

Any RuntimeException triggers rollback, and any checked Exception does not.

You can change these default settings; the various attributes of the <tx:method/> tags
that are nested within <tx:advice/> and <tx:attributes/> tags are summarized below:

Table 1. <tx:method/> settings

Attribute

Required?

Default

Description

name

Yes

Method name(s) with which the transaction attributes are to be associated. The
wildcard (*) character can be used to associate the same transaction attribute
settings with a number of methods; for example, get*, handle*, on*Event, and so
forth.

propagation

No

REQUIRED

Transaction propagation behavior.

isolation

No

DEFAULT

Transaction isolation level. Only applicable to propagation REQUIRED or REQUIRES_NEW.

timeout

No

-1

Transaction timeout (seconds). Only applicable to propagation REQUIRED or REQUIRES_NEW.

read-only

No

false

Read/write vs. read-only transaction. Only applicable to REQUIRED or REQUIRES_NEW.

Exception(s) that do not trigger rollback; comma-delimited. For example,
com.foo.MyBusinessException,ServletException.

1.5.6. Using @Transactional

In addition to the XML-based declarative approach to transaction configuration, you can
use an annotation-based approach. Declaring transaction semantics directly in the Java
source code puts the declarations much closer to the affected code. There is not much
danger of undue coupling, because code that is meant to be used transactionally is
almost always deployed that way anyway.

The standard javax.transaction.Transactional annotation is also supported as a drop-in
replacement to Spring’s own annotation. Please refer to JTA 1.2 documentation for more
details.

The ease-of-use afforded by the use of the @Transactional annotation is best
illustrated with an example, which is explained in the text that follows. Consider the
following class definition:

When the above POJO is defined as a bean in a Spring IoC container, the bean instance
can be made transactional by adding merely one line of XML configuration:

<!-- from the file 'context.xml' --><?xml version="1.0" encoding="UTF-8"?><beansxmlns="http://www.springframework.org/schema/beans"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xmlns:aop="http://www.springframework.org/schema/aop"xmlns:tx="http://www.springframework.org/schema/tx"xsi:schemaLocation="http://www.springframework.org/schema/beanshttp://www.springframework.org/schema/beans/spring-beans.xsdhttp://www.springframework.org/schema/txhttp://www.springframework.org/schema/tx/spring-tx.xsdhttp://www.springframework.org/schema/aophttp://www.springframework.org/schema/aop/spring-aop.xsd"><!-- this is the service object that we want to make transactional --><beanid="fooService"class="x.y.service.DefaultFooService"/><!-- enable the configuration of transactional behavior based on annotations --><tx:annotation-driventransaction-manager="txManager"/><!-- a PlatformTransactionManager is still required --><beanid="txManager"class="org.springframework.jdbc.datasource.DataSourceTransactionManager"><!-- (this dependency is defined somewhere else) --><propertyname="dataSource"ref="dataSource"/></bean><!-- other <bean/> definitions here --></beans>

You can omit the transaction-manager attribute in the <tx:annotation-driven/> tag if
the bean name of the PlatformTransactionManager that you want to wire in has the name
transactionManager. If the PlatformTransactionManager bean that you want to
dependency-inject has any other name, then you have to use the transaction-manager
attribute explicitly, as in the preceding example.

The @EnableTransactionManagement annotation provides equivalent support if you are
using Java based configuration. Simply add the annotation to a @Configuration class.
See the javadocs for full details.

Method visibility and @Transactional

When using proxies, you should apply the @Transactional annotation only to methods
with public visibility. If you do annotate protected, private or package-visible
methods with the @Transactional annotation, no error is raised, but the annotated
method does not exhibit the configured transactional settings. Consider the use of
AspectJ (see below) if you need to annotate non-public methods.

You can place the @Transactional annotation before an interface definition, a method
on an interface, a class definition, or a public method on a class. However, the
mere presence of the @Transactional annotation is not enough to activate the
transactional behavior. The @Transactional annotation is simply metadata that can be
consumed by some runtime infrastructure that is @Transactional-aware and that can use
the metadata to configure the appropriate beans with transactional behavior. In the
preceding example, the <tx:annotation-driven/> element switches on the
transactional behavior.

Spring recommends that you only annotate concrete classes (and methods of concrete
classes) with the @Transactional annotation, as opposed to annotating interfaces. You
certainly can place the @Transactional annotation on an interface (or an interface
method), but this works only as you would expect it to if you are using interface-based
proxies. The fact that Java annotations are not inherited from interfaces means that
if you are using class-based proxies ( proxy-target-class="true") or the weaving-based
aspect ( mode="aspectj"), then the transaction settings are not recognized by the
proxying and weaving infrastructure, and the object will not be wrapped in a
transactional proxy, which would be decidedly bad.

In proxy mode (which is the default), only external method calls coming in through the
proxy are intercepted. This means that self-invocation, in effect, a method within the
target object calling another method of the target object, will not lead to an actual
transaction at runtime even if the invoked method is marked with @Transactional. Also,
the proxy must be fully initialized to provide the expected behaviour so you should not
rely on this feature in your initialization code, i.e. @PostConstruct.

Consider the use of AspectJ mode (see mode attribute in table below) if you expect
self-invocations to be wrapped with transactions as well. In this case, there will not
be a proxy in the first place; instead, the target class will be weaved (that is, its
byte code will be modified) in order to turn @Transactional into runtime behavior on
any kind of method.

Table 2. Annotation driven transaction settings

XML Attribute

Annotation Attribute

Default

Description

transaction-manager

N/A (See TransactionManagementConfigurer javadocs)

transactionManager

Name of transaction manager to use. Only required if the name of the transaction
manager is not transactionManager, as in the example above.

mode

mode

proxy

The default mode "proxy" processes annotated beans to be proxied using Spring’s AOP
framework (following proxy semantics, as discussed above, applying to method calls
coming in through the proxy only). The alternative mode "aspectj" instead weaves the
affected classes with Spring’s AspectJ transaction aspect, modifying the target class
byte code to apply to any kind of method call. AspectJ weaving requires
spring-aspects.jar in the classpath as well as load-time weaving (or compile-time
weaving) enabled. (See Spring configuration
for details on how to set up load-time weaving.)

proxy-target-class

proxyTargetClass

false

Applies to proxy mode only. Controls what type of transactional proxies are created
for classes annotated with the @Transactional annotation. If the
proxy-target-class attribute is set to true, then class-based proxies are created.
If proxy-target-class is false or if the attribute is omitted, then standard JDK
interface-based proxies are created. (See Proxying mechanisms
for a detailed examination of the different proxy types.)

order

order

Ordered.LOWEST_PRECEDENCE

Defines the order of the transaction advice that is applied to beans annotated with
@Transactional. (For more information about the rules related to ordering of AOP
advice, see Advice ordering.)
No specified ordering means that the AOP subsystem determines the order of the advice.

The default advice mode for processing @Transactional annotations is "proxy" which
allows for interception of calls through the proxy only; local calls within the same
class cannot get intercepted that way. For a more advanced mode of interception,
consider switching to "aspectj" mode in combination with compile/load-time weaving.

The proxy-target-class attribute controls what type of transactional proxies are
created for classes annotated with the @Transactional annotation. If
proxy-target-class is set to true, class-based proxies are created. If
proxy-target-class is false or if the attribute is omitted, standard JDK
interface-based proxies are created. (See [aop-proxying] for a discussion of the
different proxy types.)

@EnableTransactionManagement and <tx:annotation-driven/> only looks for
@Transactional on beans in the same application context they are defined in. This
means that, if you put annotation driven configuration in a WebApplicationContext for
a DispatcherServlet, it only checks for @Transactional beans in your controllers,
and not your services. See MVC for more information.

The most derived location takes precedence when evaluating the transactional settings
for a method. In the case of the following example, the DefaultFooService class is
annotated at the class level with the settings for a read-only transaction, but the
@Transactional annotation on the updateFoo(Foo) method in the same class takes
precedence over the transactional settings defined at the class level.

@Transactional settings

The @Transactional annotation is metadata that specifies that an interface, class, or
method must have transactional semantics; for example, "start a brand new read-only
transaction when this method is invoked, suspending any existing transaction". The
default @Transactional settings are as follows:

Propagation setting is PROPAGATION_REQUIRED.

Isolation level is ISOLATION_DEFAULT.

Transaction is read/write.

Transaction timeout defaults to the default timeout of the underlying transaction
system, or to none if timeouts are not supported.

Any RuntimeException triggers rollback, and any checked Exception does not.

These default settings can be changed; the various properties of the @Transactional
annotation are summarized in the following table:

Optional isolation level. Only applicable to propagation REQUIRED or REQUIRES_NEW.

timeout

int (in seconds granularity)

Optional transaction timeout. Only applicable to propagation REQUIRED or REQUIRES_NEW.

readOnly

boolean

Read/write vs. read-only transaction. Only applicable to REQUIRED or REQUIRES_NEW.

rollbackFor

Array of Class objects, which must be derived from Throwable.

Optional array of exception classes that must cause rollback.

rollbackForClassName

Array of class names. Classes must be derived from Throwable.

Optional array of names of exception classes that must cause rollback.

noRollbackFor

Array of Class objects, which must be derived from Throwable.

Optional array of exception classes that must not cause rollback.

noRollbackForClassName

Array of String class names, which must be derived from Throwable.

Optional array of names of exception classes that must not cause rollback.

Currently you cannot have explicit control over the name of a transaction, where 'name'
means the transaction name that will be shown in a transaction monitor, if applicable
(for example, WebLogic’s transaction monitor), and in logging output. For declarative
transactions, the transaction name is always the fully-qualified class name + "."
+ method name of the transactionally-advised class. For example, if the
handlePayment(..) method of the BusinessService class started a transaction, the
name of the transaction would be: com.foo.BusinessService.handlePayment.

Multiple Transaction Managers with @Transactional

Most Spring applications only need a single transaction manager, but there may be
situations where you want multiple independent transaction managers in a single
application. The value attribute of the @Transactional annotation can be used to
optionally specify the identity of the PlatformTransactionManager to be used. This can
either be the bean name or the qualifier value of the transaction manager bean. For
example, using the qualifier notation, the following Java code

In this case, the two methods on TransactionalService will run under separate
transaction managers, differentiated by the "order" and "account" qualifiers. The
default <tx:annotation-driven> target bean name transactionManager will still be
used if no specifically qualified PlatformTransactionManager bean is found.

Custom shortcut annotations

If you find you are repeatedly using the same attributes with @Transactional on many
different methods, then Spring’s meta-annotation support allows
you to define custom shortcut annotations for your specific use cases. For example,
defining the following annotations

Here we have used the syntax to define the transaction manager qualifier, but could also
have included propagation behavior, rollback rules, timeouts etc.

1.5.7. Transaction propagation

This section describes some semantics of transaction propagation in Spring. Please note
that this section is not an introduction to transaction propagation proper; rather it
details some of the semantics regarding transaction propagation in Spring.

In Spring-managed transactions, be aware of the difference between physical and
logical transactions, and how the propagation setting applies to this difference.

Required

PROPAGATION_REQUIRED

PROPAGATION_REQUIRED enforces a physical transaction: either locally for the current
scope if no transaction exists yet, or participating in an existing 'outer' transaction
defined for a larger scope. This is a fine default in common call stack arrangements
within the same thread, e.g. a service facade delegating to several repository methods
where all the underlying resources have to participate in the service-level transaction.

By default, a participating transaction will join the characteristics of the outer scope,
silently ignoring the local isolation level, timeout value or read-only flag (if any).
Consider switching the "validateExistingTransactions" flag to "true" on your transaction
manager if you’d like isolation level declarations to get rejected when participating in
an existing transaction with a different isolation level. This non-lenient mode will also
reject read-only mismatches, i.e. an inner read-write transaction trying to participate
in a read-only outer scope.

When the propagation setting is PROPAGATION_REQUIRED, a logical transaction scope
is created for each method upon which the setting is applied. Each such logical
transaction scope can determine rollback-only status individually, with an outer
transaction scope being logically independent from the inner transaction scope.
Of course, in case of standard PROPAGATION_REQUIRED behavior, all these scopes will be
mapped to the same physical transaction. So a rollback-only marker set in the inner
transaction scope does affect the outer transaction’s chance to actually commit (as you
would expect it to).

However, in the case where an inner transaction scope sets the rollback-only marker, the
outer transaction has not decided on the rollback itself, and so the rollback (silently
triggered by the inner transaction scope) is unexpected. A corresponding
UnexpectedRollbackException is thrown at that point. This is expected behavior so
that the caller of a transaction can never be misled to assume that a commit was
performed when it really was not. So if an inner transaction (of which the outer caller
is not aware) silently marks a transaction as rollback-only, the outer caller still
calls commit. The outer caller needs to receive an UnexpectedRollbackException to
indicate clearly that a rollback was performed instead.

RequiresNew

PROPAGATION_REQUIRES_NEW

PROPAGATION_REQUIRES_NEW, in contrast to PROPAGATION_REQUIRED, always uses an
independent physical transaction for each affected transaction scope, never
participating in an existing transaction for an outer scope. In such an arrangement,
the underlying resource transactions are different and hence can commit or roll back
independently, with an outer transaction not affected by an inner transaction’s rollback
status, and with an inner transaction’s locks released immediately after its completion.
Such an independent inner transaction may also declare its own isolation level, timeout
and read-only settings, never inheriting an outer transaction’s characteristics.

Nested

PROPAGATION_NESTED uses a single physical transaction with multiple savepoints
that it can roll back to. Such partial rollbacks allow an inner transaction scope to
trigger a rollback for its scope, with the outer transaction being able to continue
the physical transaction despite some operations having been rolled back. This setting
is typically mapped onto JDBC savepoints, so will only work with JDBC resource
transactions. See Spring’s DataSourceTransactionManager.

1.5.8. Advising transactional operations

Suppose you want to execute both transactional and some basic profiling advice.
How do you effect this in the context of <tx:annotation-driven/>?

When you invoke the updateFoo(Foo) method, you want to see the following actions:

<?xml version="1.0" encoding="UTF-8"?><beansxmlns="http://www.springframework.org/schema/beans"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xmlns:aop="http://www.springframework.org/schema/aop"xmlns:tx="http://www.springframework.org/schema/tx"xsi:schemaLocation="http://www.springframework.org/schema/beanshttp://www.springframework.org/schema/beans/spring-beans.xsdhttp://www.springframework.org/schema/txhttp://www.springframework.org/schema/tx/spring-tx.xsdhttp://www.springframework.org/schema/aophttp://www.springframework.org/schema/aop/spring-aop.xsd"><beanid="fooService"class="x.y.service.DefaultFooService"/><!-- this is the aspect --><beanid="profiler"class="x.y.SimpleProfiler"><!-- execute before the transactional advice (hence the lower order number) --><propertyname="order"value="1"/></bean><tx:annotation-driventransaction-manager="txManager"order="200"/><aop:config><!-- this advice will execute around the transactional advice --><aop:aspectid="profilingAspect"ref="profiler"><aop:pointcutid="serviceMethodWithReturnValue"expression="execution(!void x.y..*Service.*(..))"/><aop:aroundmethod="profile"pointcut-ref="serviceMethodWithReturnValue"/></aop:aspect></aop:config><beanid="dataSource"class="org.apache.commons.dbcp.BasicDataSource"destroy-method="close"><propertyname="driverClassName"value="oracle.jdbc.driver.OracleDriver"/><propertyname="url"value="jdbc:oracle:thin:@rj-t42:1521:elvis"/><propertyname="username"value="scott"/><propertyname="password"value="tiger"/></bean><beanid="txManager"class="org.springframework.jdbc.datasource.DataSourceTransactionManager"><propertyname="dataSource"ref="dataSource"/></bean></beans>

The result of the above configuration is a fooService bean that has profiling and
transactional aspects applied to it in the desired order. You configure any number
of additional aspects in similar fashion.

The following example effects the same setup as above, but uses the purely XML
declarative approach.

<?xml version="1.0" encoding="UTF-8"?><beansxmlns="http://www.springframework.org/schema/beans"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xmlns:aop="http://www.springframework.org/schema/aop"xmlns:tx="http://www.springframework.org/schema/tx"xsi:schemaLocation="http://www.springframework.org/schema/beanshttp://www.springframework.org/schema/beans/spring-beans.xsdhttp://www.springframework.org/schema/txhttp://www.springframework.org/schema/tx/spring-tx.xsdhttp://www.springframework.org/schema/aophttp://www.springframework.org/schema/aop/spring-aop.xsd"><beanid="fooService"class="x.y.service.DefaultFooService"/><!-- the profiling advice --><beanid="profiler"class="x.y.SimpleProfiler"><!-- execute before the transactional advice (hence the lower order number) --><propertyname="order"value="1"/></bean><aop:config><aop:pointcutid="entryPointMethod"expression="execution(* x.y..*Service.*(..))"/><!-- will execute after the profiling advice (c.f. the order attribute) --><aop:advisoradvice-ref="txAdvice"pointcut-ref="entryPointMethod"order="2"/><!-- order value is higher than the profiling aspect --><aop:aspectid="profilingAspect"ref="profiler"><aop:pointcutid="serviceMethodWithReturnValue"expression="execution(!void x.y..*Service.*(..))"/><aop:aroundmethod="profile"pointcut-ref="serviceMethodWithReturnValue"/></aop:aspect></aop:config><tx:adviceid="txAdvice"transaction-manager="txManager"><tx:attributes><tx:methodname="get*"read-only="true"/><tx:methodname="*"/></tx:attributes></tx:advice><!-- other <bean/> definitions such as a DataSource and a PlatformTransactionManager here --></beans>

The result of the above configuration will be a fooService bean that has profiling and
transactional aspects applied to it in that order. If you want the profiling advice
to execute after the transactional advice on the way in, and before the
transactional advice on the way out, then you simply swap the value of the profiling
aspect bean’s order property so that it is higher than the transactional advice’s
order value.

You configure additional aspects in similar fashion.

1.5.9. Using @Transactional with AspectJ

It is also possible to use the Spring Framework’s @Transactional support outside of a
Spring container by means of an AspectJ aspect. To do so, you first annotate your
classes (and optionally your classes' methods) with the @Transactional annotation, and
then you link (weave) your application with the
org.springframework.transaction.aspectj.AnnotationTransactionAspect defined in the
spring-aspects.jar file. The aspect must also be configured with a transaction
manager. You can of course use the Spring Framework’s IoC container to take care of
dependency-injecting the aspect. The simplest way to configure the transaction
management aspect is to use the <tx:annotation-driven/> element and specify the mode
attribute to aspectj as described in Using @Transactional. Because
we’re focusing here on applications running outside of a Spring container, we’ll show
you how to do it programmatically.

// construct an appropriate transaction manager
DataSourceTransactionManager txManager = new DataSourceTransactionManager(getDataSource());
// configure the AnnotationTransactionAspect to use it; this must be done before executing any transactional methods
AnnotationTransactionAspect.aspectOf().setTransactionManager(txManager);

When using this aspect, you must annotate the implementation class (and/or methods
within that class), not the interface (if any) that the class implements. AspectJ
follows Java’s rule that annotations on interfaces are not inherited.

The @Transactional annotation on a class specifies the default transaction semantics
for the execution of any public method in the class.

The @Transactional annotation on a method within the class overrides the default
transaction semantics given by the class annotation (if present). Any method may be
annotated, regardless of visibility.

1.6. Programmatic transaction management

The Spring Framework provides two means of programmatic transaction management:

Using the TransactionTemplate.

Using a PlatformTransactionManager implementation directly.

The Spring team generally recommends the TransactionTemplate for programmatic
transaction management. The second approach is similar to using the JTA
UserTransaction API, although exception handling is less cumbersome.

1.6.1. Using the TransactionTemplate

The TransactionTemplate adopts the same approach as other Spring templates such as
the JdbcTemplate. It uses a callback approach, to free application code from having to
do the boilerplate acquisition and release of transactional resources, and results in
code that is intention driven, in that the code that is written focuses solely on what
the developer wants to do.

As you will see in the examples that follow, using the TransactionTemplate absolutely
couples you to Spring’s transaction infrastructure and APIs. Whether or not programmatic
transaction management is suitable for your development needs is a decision that you
will have to make yourself.

Application code that must execute in a transactional context, and that will use the
TransactionTemplate explicitly, looks like the following. You, as an application
developer, write a TransactionCallback implementation (typically expressed as an
anonymous inner class) that contains the code that you need to execute in the context of
a transaction. You then pass an instance of your custom TransactionCallback to the
execute(..) method exposed on the TransactionTemplate.

Specifying transaction settings

You can specify transaction settings such as the propagation mode, the isolation level,
the timeout, and so forth on the TransactionTemplate either programmatically or in
configuration. TransactionTemplate instances by default have the
default transactional settings. The
following example shows the programmatic customization of the transactional settings for
a specific TransactionTemplate:

publicclassSimpleServiceimplements Service {
privatefinal TransactionTemplate transactionTemplate;
public SimpleService(PlatformTransactionManager transactionManager) {
this.transactionTemplate = new TransactionTemplate(transactionManager);
// the transaction settings can be set here explicitly if so desiredthis.transactionTemplate.setIsolationLevel(TransactionDefinition.ISOLATION_READ_UNCOMMITTED);
this.transactionTemplate.setTimeout(30); // 30 seconds// and so forth...
}
}

The following example defines a TransactionTemplate with some custom transactional
settings, using Spring XML configuration. The sharedTransactionTemplate can then be
injected into as many services as are required.

Finally, instances of the TransactionTemplate class are threadsafe, in that instances
do not maintain any conversational state. TransactionTemplate instances do however
maintain configuration state, so while a number of classes may share a single instance
of a TransactionTemplate, if a class needs to use a TransactionTemplate with
different settings (for example, a different isolation level), then you need to create
two distinct TransactionTemplate instances.

1.6.2. Using the PlatformTransactionManager

You can also use the org.springframework.transaction.PlatformTransactionManager
directly to manage your transaction. Simply pass the implementation of the
PlatformTransactionManager you are using to your bean through a bean reference. Then,
using the TransactionDefinition and TransactionStatus objects you can initiate
transactions, roll back, and commit.

Programmatic transaction management is usually a good idea only if you have a small
number of transactional operations. For example, if you have a web application that
require transactions only for certain update operations, you may not want to set up
transactional proxies using Spring or any other technology. In this case, using the
TransactionTemplatemay be a good approach. Being able to set the transaction name
explicitly is also something that can only be done using the programmatic approach to
transaction management.

On the other hand, if your application has numerous transactional operations,
declarative transaction management is usually worthwhile. It keeps transaction
management out of business logic, and is not difficult to configure. When using the
Spring Framework, rather than EJB CMT, the configuration cost of declarative transaction
management is greatly reduced.

1.8. Transaction bound event

As of Spring 4.2, the listener of an event can be bound to a phase of the transaction. The
typical example is to handle the event when the transaction has completed successfully: this
allows events to be used with more flexibility when the outcome of the current transaction
actually matters to the listener.

Registering a regular event listener is done via the @EventListener annotation. If you need
to bind it to the transaction use @TransactionalEventListener. When you do so, the listener
will be bound to the commit phase of the transaction by default.

Let’s take an example to illustrate this concept. Assume that a component publishes an order
created event and we want to define a listener that should only handle that event once the
transaction in which it has been published has committed successfully:

The TransactionalEventListener annotation exposes a phase attribute that allows us to customize
which phase of the transaction the listener should be bound to. The valid phases are BEFORE_COMMIT,
AFTER_COMMIT (default), AFTER_ROLLBACK and AFTER_COMPLETION that aggregates the transaction
completion (be it a commit or a rollback).

If no transaction is running, the listener is not invoked at all since we can’t honor the required
semantics. It is however possible to override that behaviour by setting the fallbackExecution attribute
of the annotation to true.

1.9. Application server-specific integration

Spring’s transaction abstraction generally is application server agnostic. Additionally,
Spring’s JtaTransactionManager class, which can optionally perform a JNDI lookup for
the JTA UserTransaction and TransactionManager objects, autodetects the location for
the latter object, which varies by application server. Having access to the JTA
TransactionManager allows for enhanced transaction semantics, in particular supporting
transaction suspension. See the JtaTransactionManager javadocs for details.

Spring’s JtaTransactionManager is the standard choice to run on Java EE application
servers, and is known to work on all common servers. Advanced functionality such as
transaction suspension works on many servers as well — including GlassFish, JBoss and
Geronimo — without any special configuration required. However, for fully supported
transaction suspension and further advanced integration, Spring ships special adapters
for WebLogic Server and WebSphere. These adapters are discussed in the following
sections.

For standard scenarios, including WebLogic Server and WebSphere, consider using the
convenient <tx:jta-transaction-manager/> configuration element. When configured,
this element automatically detects the underlying server and chooses the best
transaction manager available for the platform. This means that you won’t have to
configure server-specific adapter classes (as discussed in the following sections)
explicitly; rather, they are chosen automatically, with the standard
JtaTransactionManager as default fallback.

1.9.1. IBM WebSphere

On WebSphere 6.1.0.9 and above, the recommended Spring JTA transaction manager to use is
WebSphereUowTransactionManager. This special adapter leverages IBM’s UOWManager API,
which is available in WebSphere Application Server 6.1.0.9 and later. With this adapter,
Spring-driven transaction suspension (suspend/resume as initiated by
PROPAGATION_REQUIRES_NEW) is officially supported by IBM.

1.9.2. Oracle WebLogic Server

On WebLogic Server 9.0 or above, you typically would use the
WebLogicJtaTransactionManager instead of the stock JtaTransactionManager class. This
special WebLogic-specific subclass of the normal JtaTransactionManager supports the
full power of Spring’s transaction definitions in a WebLogic-managed transaction
environment, beyond standard JTA semantics: Features include transaction names,
per-transaction isolation levels, and proper resuming of transactions in all cases.

1.10. Solutions to common problems

1.10.1. Use of the wrong transaction manager for a specific DataSource

Use the correctPlatformTransactionManager implementation based on your choice of
transactional technologies and requirements. Used properly, the Spring Framework merely
provides a straightforward and portable abstraction. If you are using global
transactions, you must use the
org.springframework.transaction.jta.JtaTransactionManager class (or an
application server-specific subclass of
it) for all your transactional operations. Otherwise the transaction infrastructure
attempts to perform local transactions on resources such as container DataSource
instances. Such local transactions do not make sense, and a good application server
treats them as errors.

1.11. Further resources

For more information about the Spring Framework’s transaction support:

Java Transaction Design Strategies is a book
available from InfoQ that provides a well-paced introduction
to transactions in Java. It also includes side-by-side examples of how to configure
and use transactions with both the Spring Framework and EJB3.

2. DAO support

2.1. Introduction

The Data Access Object (DAO) support in Spring is aimed at making it easy to work with
data access technologies like JDBC, Hibernate or JPA in a consistent way. This
allows one to switch between the aforementioned persistence technologies fairly easily
and it also allows one to code without worrying about catching exceptions that are
specific to each technology.

2.2. Consistent exception hierarchy

Spring provides a convenient translation from technology-specific exceptions like
SQLException to its own exception class hierarchy with the DataAccessException as
the root exception. These exceptions wrap the original exception so there is never any
risk that one might lose any information as to what might have gone wrong.

In addition to JDBC exceptions, Spring can also wrap Hibernate-specific exceptions,
converting them to a set of focused runtime exceptions (the same is true for JPA
exceptions). This allows one to handle most persistence exceptions, which are
non-recoverable, only in the appropriate layers, without having annoying boilerplate
catch-and-throw blocks and exception declarations in one’s DAOs. (One can still trap
and handle exceptions anywhere one needs to though.) As mentioned above, JDBC
exceptions (including database-specific dialects) are also converted to the same
hierarchy, meaning that one can perform some operations with JDBC within a consistent
programming model.

The above holds true for the various template classes in Springs support for various ORM
frameworks. If one uses the interceptor-based classes then the application must care
about handling HibernateExceptions and PersistenceExceptions itself, preferably via
delegating to SessionFactoryUtils’ `convertHibernateAccessException(..) or
convertJpaAccessException() methods respectively. These methods convert the exceptions
to ones that are compatible with the exceptions in the org.springframework.dao
exception hierarchy. As PersistenceExceptions are unchecked, they can simply get
thrown too, sacrificing generic DAO abstraction in terms of exceptions though.

The exception hierarchy that Spring provides can be seen below. (Please note that the
class hierarchy detailed in the image shows only a subset of the entire
DataAccessException hierarchy.)

2.3. Annotations used for configuring DAO or Repository classes

The best way to guarantee that your Data Access Objects (DAOs) or repositories provide
exception translation is to use the @Repository annotation. This annotation also
allows the component scanning support to find and configure your DAOs and repositories
without having to provide XML configuration entries for them.

Any DAO or repository implementation will need to access to a persistence resource,
depending on the persistence technology used; for example, a JDBC-based repository will
need access to a JDBC DataSource; a JPA-based repository will need access to an
EntityManager. The easiest way to accomplish this is to have this resource dependency
injected using one of the @Autowired,, @Inject, @Resource or @PersistenceContext
annotations. Here is an example for a JPA repository:

Last example we will show here is for typical JDBC support. You would have the
DataSource injected into an initialization method where you would create a
JdbcTemplate and other data access support classes like SimpleJdbcCall etc using
this DataSource.

Please see the specific coverage of each persistence technology for details on how to
configure the application context to take advantage of these annotations.

3. Data access with JDBC

3.1. Introduction to Spring Framework JDBC

The value-add provided by the Spring Framework JDBC abstraction is perhaps best shown by
the sequence of actions outlined in the table below. The table shows what actions Spring
will take care of and which actions are the responsibility of you, the application
developer.

Table 4. Spring JDBC - who does what?

Action

Spring

You

Define connection parameters.

X

Open the connection.

X

Specify the SQL statement.

X

Declare parameters and provide parameter values

X

Prepare and execute the statement.

X

Set up the loop to iterate through the results (if any).

X

Do the work for each iteration.

X

Process any exception.

X

Handle transactions.

X

Close the connection, statement and resultset.

X

The Spring Framework takes care of all the low-level details that can make JDBC such a
tedious API to develop with.

3.1.1. Choosing an approach for JDBC database access

You can choose among several approaches to form the basis for your JDBC database access.
In addition to three flavors of the JdbcTemplate, a new SimpleJdbcInsert and
SimplejdbcCall approach optimizes database metadata, and the RDBMS Object style takes a
more object-oriented approach similar to that of JDO Query design. Once you start using
one of these approaches, you can still mix and match to include a feature from a
different approach. All approaches require a JDBC 2.0-compliant driver, and some
advanced features require a JDBC 3.0 driver.

JdbcTemplate is the classic Spring JDBC approach and the most popular. This
"lowest level" approach and all others use a JdbcTemplate under the covers.

NamedParameterJdbcTemplate wraps a JdbcTemplate to provide named parameters
instead of the traditional JDBC "?" placeholders. This approach provides better
documentation and ease of use when you have multiple parameters for an SQL statement.

SimpleJdbcInsert and SimpleJdbcCall optimize database metadata to limit the amount
of necessary configuration. This approach simplifies coding so that you only need to
provide the name of the table or procedure and provide a map of parameters matching
the column names. This only works if the database provides adequate metadata. If the
database doesn’t provide this metadata, you will have to provide explicit
configuration of the parameters.

RDBMS Objects including MappingSqlQuery, SqlUpdate and StoredProcedure requires
you to create reusable and thread-safe objects during initialization of your data
access layer. This approach is modeled after JDO Query wherein you define your query
string, declare parameters, and compile the query. Once you do that, execute methods
can be called multiple times with various parameter values passed in.

The org.springframework.jdbc.datasource package contains a utility class for easy
DataSource access, and various simple DataSource implementations that can be used for
testing and running unmodified JDBC code outside of a Java EE container. A subpackage
named org.springfamework.jdbc.datasource.embedded provides support for creating
embedded databases using Java database engines such as HSQL, H2, and Derby. See
Controlling database connections and Embedded database support.

The org.springframework.jdbc.object package contains classes that represent RDBMS
queries, updates, and stored procedures as thread-safe, reusable objects. See
Modeling JDBC operations as Java objects. This approach is modeled by JDO, although objects returned by queries
are naturally disconnected from the database. This higher level of JDBC abstraction
depends on the lower-level abstraction in the org.springframework.jdbc.core package.

The org.springframework.jdbc.support package provides SQLException translation
functionality and some utility classes. Exceptions thrown during JDBC processing are
translated to exceptions defined in the org.springframework.dao package. This means
that code using the Spring JDBC abstraction layer does not need to implement JDBC or
RDBMS-specific error handling. All translated exceptions are unchecked, which gives you
the option of catching the exceptions from which you can recover while allowing other
exceptions to be propagated to the caller. See SQLExceptionTranslator.

3.2. Using the JDBC core classes to control basic JDBC processing and error handling

3.2.1. JdbcTemplate

The JdbcTemplate class is the central class in the JDBC core package. It handles the
creation and release of resources, which helps you avoid common errors such as
forgetting to close the connection. It performs the basic tasks of the core JDBC
workflow such as statement creation and execution, leaving application code to provide
SQL and extract results. The JdbcTemplate class executes SQL queries, update
statements and stored procedure calls, performs iteration over ResultSets and
extraction of returned parameter values. It also catches JDBC exceptions and translates
them to the generic, more informative, exception hierarchy defined in the
org.springframework.dao package.

When you use the JdbcTemplate for your code, you only need to implement callback
interfaces, giving them a clearly defined contract. The PreparedStatementCreator
callback interface creates a prepared statement given a Connection provided by this
class, providing SQL and any necessary parameters. The same is true for the
CallableStatementCreator interface, which creates callable statements. The
RowCallbackHandler interface extracts values from each row of a ResultSet.

The JdbcTemplate can be used within a DAO implementation through direct instantiation
with a DataSource reference, or be configured in a Spring IoC container and given to
DAOs as a bean reference.

The DataSource should always be configured as a bean in the Spring IoC container. In
the first case the bean is given to the service directly; in the second case it is given
to the prepared template.

All SQL issued by this class is logged at the DEBUG level under the category
corresponding to the fully qualified class name of the template instance (typically
JdbcTemplate, but it may be different if you are using a custom subclass of the
JdbcTemplate class).

Examples of JdbcTemplate class usage

This section provides some examples of JdbcTemplate class usage. These examples are
not an exhaustive list of all of the functionality exposed by the JdbcTemplate; see
the attendant javadocs for that.

If the last two snippets of code actually existed in the same application, it would make
sense to remove the duplication present in the two RowMapper anonymous inner classes,
and extract them out into a single class (typically a static nested class) that can
then be referenced by DAO methods as needed. For example, it may be better to write the
last code snippet as follows:

Other JdbcTemplate operations

You can use the execute(..) method to execute any arbitrary SQL, and as such the
method is often used for DDL statements. It is heavily overloaded with variants taking
callback interfaces, binding variable arrays, and so on.

JdbcTemplate best practices

Instances of the JdbcTemplate class are threadsafe once configured. This is
important because it means that you can configure a single instance of a JdbcTemplate
and then safely inject this shared reference into multiple DAOs (or repositories).
The JdbcTemplate is stateful, in that it maintains a reference to a DataSource, but
this state is not conversational state.

A common practice when using the JdbcTemplate class (and the associated
NamedParameterJdbcTemplate classes) is to
configure a DataSource in your Spring configuration file, and then dependency-inject
that shared DataSource bean into your DAO classes; the JdbcTemplate is created in
the setter for the DataSource. This leads to DAOs that look in part like the following:

An alternative to explicit configuration is to use component-scanning and annotation
support for dependency injection. In this case you annotate the class with @Repository
(which makes it a candidate for component-scanning) and annotate the DataSource setter
method with @Autowired.

The corresponding XML configuration file would look like the following:

<?xml version="1.0" encoding="UTF-8"?><beansxmlns="http://www.springframework.org/schema/beans"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xmlns:context="http://www.springframework.org/schema/context"xsi:schemaLocation="http://www.springframework.org/schema/beanshttp://www.springframework.org/schema/beans/spring-beans.xsdhttp://www.springframework.org/schema/contexthttp://www.springframework.org/schema/context/spring-context.xsd"><!-- Scans within the base package of the application for @Component classes to configure as beans --><context:component-scanbase-package="org.springframework.docs.test"/><beanid="dataSource"class="org.apache.commons.dbcp.BasicDataSource"destroy-method="close"><propertyname="driverClassName"value="${jdbc.driverClassName}"/><propertyname="url"value="${jdbc.url}"/><propertyname="username"value="${jdbc.username}"/><propertyname="password"value="${jdbc.password}"/></bean><context:property-placeholderlocation="jdbc.properties"/></beans>

If you are using Spring’s JdbcDaoSupport class, and your various JDBC-backed DAO classes
extend from it, then your sub-class inherits a setDataSource(..) method from the
JdbcDaoSupport class. You can choose whether to inherit from this class. The
JdbcDaoSupport class is provided as a convenience only.

Regardless of which of the above template initialization styles you choose to use (or
not), it is seldom necessary to create a new instance of a JdbcTemplate class each
time you want to execute SQL. Once configured, a JdbcTemplate instance is threadsafe.
You may want multiple JdbcTemplate instances if your application accesses multiple
databases, which requires multiple DataSources, and subsequently multiple differently
configured JdbcTemplates.

3.2.2. NamedParameterJdbcTemplate

The NamedParameterJdbcTemplate class adds support for programming JDBC statements
using named parameters, as opposed to programming JDBC statements using only classic
placeholder ( '?') arguments. The NamedParameterJdbcTemplate class wraps a
JdbcTemplate, and delegates to the wrapped JdbcTemplate to do much of its work. This
section describes only those areas of the NamedParameterJdbcTemplate class that differ
from the JdbcTemplate itself; namely, programming JDBC statements using named
parameters.

Notice the use of the named parameter notation in the value assigned to the sql
variable, and the corresponding value that is plugged into the namedParameters
variable (of type MapSqlParameterSource).

Alternatively, you can pass along named parameters and their corresponding values to a
NamedParameterJdbcTemplate instance by using the Map-based style.The remaining
methods exposed by the NamedParameterJdbcOperations and implemented by the
NamedParameterJdbcTemplate class follow a similar pattern and are not covered here.

One nice feature related to the NamedParameterJdbcTemplate (and existing in the same
Java package) is the SqlParameterSource interface. You have already seen an example of
an implementation of this interface in one of the previous code snippet (the
MapSqlParameterSource class). An SqlParameterSource is a source of named parameter
values to a NamedParameterJdbcTemplate. The MapSqlParameterSource class is a very
simple implementation that is simply an adapter around a java.util.Map, where the keys
are the parameter names and the values are the parameter values.

Another SqlParameterSource implementation is the BeanPropertySqlParameterSource
class. This class wraps an arbitrary JavaBean (that is, an instance of a class that
adheres to the
JavaBean conventions), and uses the properties of the wrapped JavaBean as the source
of named parameter values.

Remember that the NamedParameterJdbcTemplate class wraps a classic JdbcTemplate
template; if you need access to the wrapped JdbcTemplate instance to access
functionality only present in the JdbcTemplate class, you can use the
getJdbcOperations() method to access the wrapped JdbcTemplate through the
JdbcOperations interface.

3.2.3. SQLExceptionTranslator

SQLExceptionTranslator is an interface to be implemented by classes that can translate
between SQLExceptions and Spring’s own org.springframework.dao.DataAccessException,
which is agnostic in regard to data access strategy. Implementations can be generic (for
example, using SQLState codes for JDBC) or proprietary (for example, using Oracle error
codes) for greater precision.

SQLErrorCodeSQLExceptionTranslator is the implementation of SQLExceptionTranslator
that is used by default. This implementation uses specific vendor codes. It is more
precise than the SQLState implementation. The error code translations are based on
codes held in a JavaBean type class called SQLErrorCodes. This class is created and
populated by an SQLErrorCodesFactory which as the name suggests is a factory for
creating SQLErrorCodes based on the contents of a configuration file named
sql-error-codes.xml. This file is populated with vendor codes and based on the
DatabaseProductName taken from the DatabaseMetaData. The codes for the actual
database you are using are used.

The SQLErrorCodeSQLExceptionTranslator applies matching rules in the following sequence:

The SQLErrorCodesFactory is used by default to define Error codes and custom exception
translations. They are looked up in a file named sql-error-codes.xml from the
classpath and the matching SQLErrorCodes instance is located based on the database
name from the database metadata of the database in use.

Any custom translation implemented by a subclass. Normally the provided concrete
SQLErrorCodeSQLExceptionTranslator is used so this rule does not apply. It only
applies if you have actually provided a subclass implementation.

Any custom implementation of the SQLExceptionTranslator interface that is provided
as the customSqlExceptionTranslator property of the SQLErrorCodes class.

The list of instances of the CustomSQLErrorCodesTranslation class, provided for the
customTranslations property of the SQLErrorCodes class, are searched for a match.

Error code matching is applied.

Use the fallback translator. SQLExceptionSubclassTranslator is the default fallback
translator. If this translation is not available then the next fallback translator is
the SQLStateSQLExceptionTranslator.

In this example, the specific error code -12345 is translated and other errors are
left to be translated by the default translator implementation. To use this custom
translator, it is necessary to pass it to the JdbcTemplate through the method
setExceptionTranslator and to use this JdbcTemplate for all of the data access
processing where this translator is needed. Here is an example of how this custom
translator can be used:

The custom translator is passed a data source in order to look up the error codes in
sql-error-codes.xml.

3.2.4. Executing statements

Executing an SQL statement requires very little code. You need a DataSource and a
JdbcTemplate, including the convenience methods that are provided with the
JdbcTemplate. The following example shows what you need to include for a minimal but
fully functional class that creates a new table:

3.2.5. Running queries

Some query methods return a single value. To retrieve a count or a specific value from
one row, use queryForObject(..). The latter converts the returned JDBC Type to the
Java class that is passed in as an argument. If the type conversion is invalid, then an
InvalidDataAccessApiUsageException is thrown. Here is an example that contains two
query methods, one for an int and one that queries for a String.

In addition to the single result query methods, several methods return a list with an
entry for each row that the query returned. The most generic method is
queryForList(..) which returns a List where each entry is a Map with each entry in
the map representing the column value for that row. If you add a method to the above
example to retrieve a list of all the rows, it would look like this:

3.2.6. Updating the database

The following example shows a column updated for a certain primary key. In this example,
an SQL statement has placeholders for row parameters. The parameter values can be passed
in as varargs or alternatively as an array of objects. Thus primitives should be wrapped
in the primitive wrapper classes explicitly or using auto-boxing.

3.2.7. Retrieving auto-generated keys

An update() convenience method supports the retrieval of primary keys generated by the
database. This support is part of the JDBC 3.0 standard; see Chapter 13.6 of the
specification for details. The method takes a PreparedStatementCreator as its first
argument, and this is the way the required insert statement is specified. The other
argument is a KeyHolder, which contains the generated key on successful return from the
update. There is not a standard single way to create an appropriate PreparedStatement
(which explains why the method signature is the way it is). The following example works
on Oracle but may not work on other platforms:

3.3. Controlling database connections

3.3.1. DataSource

Spring obtains a connection to the database through a DataSource. A DataSource is
part of the JDBC specification and is a generalized connection factory. It allows a
container or a framework to hide connection pooling and transaction management issues
from the application code. As a developer, you need not know details about how to
connect to the database; that is the responsibility of the administrator that sets up
the datasource. You most likely fill both roles as you develop and test code, but you do
not necessarily have to know how the production data source is configured.

When using Spring’s JDBC layer, you obtain a data source from JNDI or you configure your
own with a connection pool implementation provided by a third party. Popular
implementations are Apache Jakarta Commons DBCP and C3P0. Implementations in the Spring
distribution are meant only for testing purposes and do not provide pooling.

This section uses Spring’s DriverManagerDataSource implementation, and several
additional implementations are covered later.

Only use the DriverManagerDataSource class should only be used for testing purposes
since it does not provide pooling and will perform poorly when multiple requests for a
connection are made.

You obtain a connection with DriverManagerDataSource as you typically obtain a JDBC
connection. Specify the fully qualified classname of the JDBC driver so that the
DriverManager can load the driver class. Next, provide a URL that varies between JDBC
drivers. (Consult the documentation for your driver for the correct value.) Then provide
a username and a password to connect to the database. Here is an example of how to
configure a DriverManagerDataSource in Java code:

The following examples show the basic connectivity and configuration for DBCP and C3P0.
To learn about more options that help control the pooling features, see the product
documentation for the respective connection pooling implementations.

3.3.2. DataSourceUtils

The DataSourceUtils class is a convenient and powerful helper class that provides
static methods to obtain connections from JNDI and close connections if necessary. It
supports thread-bound connections with, for example, DataSourceTransactionManager.

3.3.3. SmartDataSource

The SmartDataSource interface should be implemented by classes that can provide a
connection to a relational database. It extends the DataSource interface to allow
classes using it to query whether the connection should be closed after a given
operation. This usage is efficient when you know that you will reuse a connection.

3.3.4. AbstractDataSource

AbstractDataSource is an abstract base class for Spring’s DataSource
implementations that implements code that is common to all DataSource implementations.
You extend the AbstractDataSource class if you are writing your own DataSource
implementation.

3.3.5. SingleConnectionDataSource

The SingleConnectionDataSource class is an implementation of the SmartDataSource
interface that wraps a singleConnection that is not closed after each use.
Obviously, this is not multi-threading capable.

If any client code calls close in the assumption of a pooled connection, as when using
persistence tools, set the suppressClose property to true. This setting returns a
close-suppressing proxy wrapping the physical connection. Be aware that you will not be
able to cast this to a native Oracle Connection or the like anymore.

This is primarily a test class. For example, it enables easy testing of code outside an
application server, in conjunction with a simple JNDI environment. In contrast to
DriverManagerDataSource, it reuses the same connection all the time, avoiding
excessive creation of physical connections.

3.3.6. DriverManagerDataSource

The DriverManagerDataSource class is an implementation of the standard DataSource
interface that configures a plain JDBC driver through bean properties, and returns a new
Connection every time.

This implementation is useful for test and stand-alone environments outside of a Java EE
container, either as a DataSource bean in a Spring IoC container, or in conjunction
with a simple JNDI environment. Pool-assuming Connection.close() calls will simply
close the connection, so any DataSource-aware persistence code should work. However,
using JavaBean-style connection pools such as commons-dbcp is so easy, even in a test
environment, that it is almost always preferable to use such a connection pool over
DriverManagerDataSource.

3.3.7. TransactionAwareDataSourceProxy

TransactionAwareDataSourceProxy is a proxy for a target DataSource, which wraps that
target DataSource to add awareness of Spring-managed transactions. In this respect, it
is similar to a transactional JNDI DataSource as provided by a Java EE server.

It is rarely desirable to use this class, except when already existing code that must be
called and passed a standard JDBC DataSource interface implementation. In this case,
it’s possible to still have this code be usable, and at the same time have this code
participating in Spring managed transactions. It is generally preferable to write your
own new code using the higher level abstractions for resource management, such as
JdbcTemplate or DataSourceUtils.

(See the TransactionAwareDataSourceProxy javadocs for more details.)

3.3.8. DataSourceTransactionManager

The DataSourceTransactionManager class is a PlatformTransactionManager
implementation for single JDBC datasources. It binds a JDBC connection from the
specified data source to the currently executing thread, potentially allowing for one
thread connection per data source.

Application code is required to retrieve the JDBC connection through
DataSourceUtils.getConnection(DataSource) instead of Java EE’s standard
DataSource.getConnection. It throws unchecked org.springframework.dao exceptions
instead of checked SQLExceptions. All framework classes like JdbcTemplate use this
strategy implicitly. If not used with this transaction manager, the lookup strategy
behaves exactly like the common one - it can thus be used in any case.

The DataSourceTransactionManager class supports custom isolation levels, and timeouts
that get applied as appropriate JDBC statement query timeouts. To support the latter,
application code must either use JdbcTemplate or call the
DataSourceUtils.applyTransactionTimeout(..) method for each created statement.

This implementation can be used instead of JtaTransactionManager in the single
resource case, as it does not require the container to support JTA. Switching between
both is just a matter of configuration, if you stick to the required connection lookup
pattern. JTA does not support custom isolation levels!

3.4. JDBC batch operations

Most JDBC drivers provide improved performance if you batch multiple calls to the same
prepared statement. By grouping updates into batches you limit the number of round trips
to the database.

3.4.1. Basic batch operations with the JdbcTemplate

You accomplish JdbcTemplate batch processing by implementing two methods of a special
interface, BatchPreparedStatementSetter, and passing that in as the second parameter
in your batchUpdate method call. Use the getBatchSize method to provide the size of
the current batch. Use the setValues method to set the values for the parameters of
the prepared statement. This method will be called the number of times that you
specified in the getBatchSize call. The following example updates the actor table
based on entries in a list. The entire list is used as the batch in this example:

If you are processing a stream of updates or reading from a file, then you might have a
preferred batch size, but the last batch might not have that number of entries. In this
case you can use the InterruptibleBatchPreparedStatementSetter interface, which allows
you to interrupt a batch once the input source is exhausted. The isBatchExhausted method
allows you to signal the end of the batch.

3.4.2. Batch operations with a List of objects

Both the JdbcTemplate and the NamedParameterJdbcTemplate provides an alternate way
of providing the batch update. Instead of implementing a special batch interface, you
provide all parameter values in the call as a list. The framework loops over these
values and uses an internal prepared statement setter. The API varies depending on
whether you use named parameters. For the named parameters you provide an array of
SqlParameterSource, one entry for each member of the batch. You can use the
SqlParameterSourceUtils.createBatch convenience methods to create this array, passing
in an array of bean-style objects (with getter methods corresponding to parameters)
and/or String-keyed Maps (containing the corresponding parameters as values).

For an SQL statement using the classic "?" placeholders, you pass in a list containing an
object array with the update values. This object array must have one entry for each
placeholder in the SQL statement, and they must be in the same order as they are defined
in the SQL statement.

All of the above batch update methods return an int array containing the number of
affected rows for each batch entry. This count is reported by the JDBC driver. If the
count is not available, the JDBC driver returns a -2 value.

In such a scenario with automatic setting of values on an underlying PreparedStatement,
the corresponding JDBC type for each value needs to be derived from the given Java type.
While this usually works well, there is a potential for issues, e.g. with Map-contained
null values: Spring will by default call ParameterMetaData.getParameterType in such a
case which may be expensive with your JDBC driver. Please make sure to use a recent driver
version, and consider setting the "spring.jdbc.getParameterType.ignore" property to "true"
(as a JVM system property or in a spring.properties file in the root of your classpath)
if you encounter a performance issue, e.g. as reported on Oracle 12c (SPR-16139).

Alternatively, simply consider specifying the corresponding JDBC types explicitly:
either via a 'BatchPreparedStatementSetter' as shown above, or via an explicit type
array given to a 'List<Object[]>' based call, or via 'registerSqlType' calls on a
custom 'MapSqlParameterSource' instance, or via a 'BeanPropertySqlParameterSource'
which derives the SQL type from the Java-declared property type even for a null value.

3.4.3. Batch operations with multiple batches

The last example of a batch update deals with batches that are so large that you want to
break them up into several smaller batches. You can of course do this with the methods
mentioned above by making multiple calls to the batchUpdate method, but there is now a
more convenient method. This method takes, in addition to the SQL statement, a
Collection of objects containing the parameters, the number of updates to make for each
batch and a ParameterizedPreparedStatementSetter to set the values for the parameters
of the prepared statement. The framework loops over the provided values and breaks the
update calls into batches of the size specified.

The batch update methods for this call returns an array of int arrays containing an array
entry for each batch with an array of the number of affected rows for each update. The top
level array’s length indicates the number of batches executed and the second level array’s
length indicates the number of updates in that batch. The number of updates in each batch
should be the batch size provided for all batches except for the last one that might
be less, depending on the total number of update objects provided. The update count for
each update statement is the one reported by the JDBC driver. If the count is not
available, the JDBC driver returns a -2 value.

3.5. Simplifying JDBC operations with the SimpleJdbc classes

The SimpleJdbcInsert and SimpleJdbcCall classes provide a simplified configuration
by taking advantage of database metadata that can be retrieved through the JDBC driver.
This means there is less to configure up front, although you can override or turn off
the metadata processing if you prefer to provide all the details in your code.

3.5.1. Inserting data using SimpleJdbcInsert

Let’s start by looking at the SimpleJdbcInsert class with the minimal amount of
configuration options. You should instantiate the SimpleJdbcInsert in the data access
layer’s initialization method. For this example, the initializing method is the
setDataSource method. You do not need to subclass the SimpleJdbcInsert class; simply
create a new instance and set the table name using the withTableName method.
Configuration methods for this class follow the "fluid" style that returns the instance
of the SimpleJdbcInsert, which allows you to chain all configuration methods. This
example uses only one configuration method; you will see examples of multiple ones later.

The execute method used here takes a plain java.utils.Map as its only parameter. The
important thing to note here is that the keys used for the Map must match the column
names of the table as defined in the database. This is because we read the metadata in
order to construct the actual insert statement.

3.5.2. Retrieving auto-generated keys using SimpleJdbcInsert

This example uses the same insert as the preceding, but instead of passing in the id it
retrieves the auto-generated key and sets it on the new Actor object. When you create
the SimpleJdbcInsert, in addition to specifying the table name, you specify the name
of the generated key column with the usingGeneratedKeyColumns method.

The main difference when executing the insert by this second approach is that you do not
add the id to the Map and you call the executeAndReturnKey method. This returns a
java.lang.Number object with which you can create an instance of the numerical type that
is used in our domain class. You cannot rely on all databases to return a specific Java
class here; java.lang.Number is the base class that you can rely on. If you have
multiple auto-generated columns, or the generated values are non-numeric, then you can
use a KeyHolder that is returned from the executeAndReturnKeyHolder method.

3.5.3. Specifying columns for a SimpleJdbcInsert

You can limit the columns for an insert by specifying a list of column names with the
usingColumns method:

The execution of the insert is the same as if you had relied on the metadata to determine
which columns to use.

3.5.4. Using SqlParameterSource to provide parameter values

Using a Map to provide parameter values works fine, but it’s not the most convenient
class to use. Spring provides a couple of implementations of the SqlParameterSource
interface that can be used instead.The first one is BeanPropertySqlParameterSource,
which is a very convenient class if you have a JavaBean-compliant class that contains
your values. It will use the corresponding getter method to extract the parameter
values. Here is an example:

As you can see, the configuration is the same; only the executing code has to change to
use these alternative input classes.

3.5.5. Calling a stored procedure with SimpleJdbcCall

The SimpleJdbcCall class leverages metadata in the database to look up names of in
and out parameters, so that you do not have to declare them explicitly. You can
declare parameters if you prefer to do that, or if you have parameters such as ARRAY
or STRUCT that do not have an automatic mapping to a Java class. The first example
shows a simple procedure that returns only scalar values in VARCHAR and DATE format
from a MySQL database. The example procedure reads a specified actor entry and returns
first_name, last_name, and birth_date columns in the form of out parameters.

The in_id parameter contains the id of the actor you are looking up. The out
parameters return the data read from the table.

The SimpleJdbcCall is declared in a similar manner to the SimpleJdbcInsert. You
should instantiate and configure the class in the initialization method of your data
access layer. Compared to the StoredProcedure class, you don’t have to create a subclass
and you don’t have to declare parameters that can be looked up in the database metadata.
Following is an example of a SimpleJdbcCall configuration using the above stored
procedure. The only configuration option, in addition to the DataSource, is the name
of the stored procedure.

The code you write for the execution of the call involves creating an SqlParameterSource
containing the IN parameter. It’s important to match the name provided for the input value
with that of the parameter name declared in the stored procedure. The case does not have
to match because you use metadata to determine how database objects should be referred to
in a stored procedure. What is specified in the source for the stored procedure is not
necessarily the way it is stored in the database. Some databases transform names to all
upper case while others use lower case or use the case as specified.

The execute method takes the IN parameters and returns a Map containing any out
parameters keyed by the name as specified in the stored procedure. In this case they are
out_first_name, out_last_name and out_birth_date.

The last part of the execute method creates an Actor instance to use to return the
data retrieved. Again, it is important to use the names of the out parameters as they
are declared in the stored procedure. Also, the case in the names of the out
parameters stored in the results map matches that of the out parameter names in the
database, which could vary between databases. To make your code more portable you should
do a case-insensitive lookup or instruct Spring to use a LinkedCaseInsensitiveMap.
To do the latter, you create your own JdbcTemplate and set the setResultsMapCaseInsensitive
property to true. Then you pass this customized JdbcTemplate instance into
the constructor of your SimpleJdbcCall. Here is an example of this configuration:

By taking this action, you avoid conflicts in the case used for the names of your
returned out parameters.

3.5.6. Explicitly declaring parameters to use for a SimpleJdbcCall

You have seen how the parameters are deduced based on metadata, but you can declare then
explicitly if you wish. You do this by creating and configuring SimpleJdbcCall with
the declareParameters method, which takes a variable number of SqlParameter objects
as input. See the next section for details on how to define an SqlParameter.

Explicit declarations are necessary if the database you use is not a Spring-supported
database. Currently Spring supports metadata lookup of stored procedure calls for the
following databases: Apache Derby, DB2, MySQL, Microsoft SQL Server, Oracle, and Sybase.
We also support metadata lookup of stored functions for MySQL, Microsoft SQL Server,
and Oracle.

You can opt to declare one, some, or all the parameters explicitly. The parameter
metadata is still used where you do not declare parameters explicitly. To bypass all
processing of metadata lookups for potential parameters and only use the declared
parameters, you call the method withoutProcedureColumnMetaDataAccess as part of the
declaration. Suppose that you have two or more different call signatures declared for a
database function. In this case you call the useInParameterNames to specify the list
of IN parameter names to include for a given signature.

The following example shows a fully declared procedure call, using the information from
the preceding example.

The execution and end results of the two examples are the same; this one specifies all
details explicitly rather than relying on metadata.

3.5.7. How to define SqlParameters

To define a parameter for the SimpleJdbc classes and also for the RDBMS operations
classes, covered in Modeling JDBC operations as Java objects, you use an SqlParameter or one of its subclasses.
You typically specify the parameter name and SQL type in the constructor. The SQL type
is specified using the java.sql.Types constants. We have already seen declarations
like:

new SqlParameter("in_id", Types.NUMERIC),
new SqlOutParameter("out_first_name", Types.VARCHAR),

The first line with the SqlParameter declares an IN parameter. IN parameters can be
used for both stored procedure calls and for queries using the SqlQuery and its
subclasses covered in the following section.

The second line with the SqlOutParameter declares an out parameter to be used in a
stored procedure call. There is also an SqlInOutParameter for InOut parameters,
parameters that provide an IN value to the procedure and that also return a value.

Only parameters declared as SqlParameter and SqlInOutParameter will be used to
provide input values. This is different from the StoredProcedure class, which for
backwards compatibility reasons allows input values to be provided for parameters
declared as SqlOutParameter.

For IN parameters, in addition to the name and the SQL type, you can specify a scale for
numeric data or a type name for custom database types. For out parameters, you can
provide a RowMapper to handle mapping of rows returned from a REF cursor. Another
option is to specify an SqlReturnType that provides an opportunity to define
customized handling of the return values.

3.5.8. Calling a stored function using SimpleJdbcCall

You call a stored function in almost the same way as you call a stored procedure, except
that you provide a function name rather than a procedure name. You use the
withFunctionName method as part of the configuration to indicate that we want to make
a call to a function, and the corresponding string for a function call is generated. A
specialized execute call, executeFunction, is used to execute the function and it
returns the function return value as an object of a specified type, which means you do
not have to retrieve the return value from the results map. A similar convenience method
named executeObject is also available for stored procedures that only have one out
parameter. The following example is based on a stored function named get_actor_name
that returns an actor’s full name. Here is the MySQL source for this function:

The execute method used returns a String containing the return value from the function
call.

3.5.9. Returning ResultSet/REF Cursor from a SimpleJdbcCall

Calling a stored procedure or function that returns a result set is a bit tricky. Some
databases return result sets during the JDBC results processing while others require an
explicitly registered out parameter of a specific type. Both approaches need
additional processing to loop over the result set and process the returned rows. With
the SimpleJdbcCall you use the returningResultSet method and declare a RowMapper
implementation to be used for a specific parameter. In the case where the result set is
returned during the results processing, there are no names defined, so the returned
results will have to match the order in which you declare the RowMapper
implementations. The name specified is still used to store the processed list of results
in the results map that is returned from the execute statement.

The next example uses a stored procedure that takes no IN parameters and returns all
rows from the t_actor table. Here is the MySQL source for this procedure:

To call this procedure you declare the RowMapper. Because the class you want to map to
follows the JavaBean rules, you can use a BeanPropertyRowMapper that is
created by passing in the required class to map to in the newInstance method.

The execute call passes in an empty Map because this call does not take any parameters.
The list of Actors is then retrieved from the results map and returned to the caller.

3.6. Modeling JDBC operations as Java objects

The org.springframework.jdbc.object package contains classes that allow you to access
the database in a more object-oriented manner. As an example, you can execute queries
and get the results back as a list containing business objects with the relational
column data mapped to the properties of the business object. You can also execute stored
procedures and run update, delete, and insert statements.

Many Spring developers believe that the various RDBMS operation classes described below
(with the exception of the StoredProcedure class) can often
be replaced with straight JdbcTemplate calls. Often it is simpler to write a DAO
method that simply calls a method on a JdbcTemplate directly (as opposed to
encapsulating a query as a full-blown class).

However, if you are getting measurable value from using the RDBMS operation classes,
continue using these classes.

3.6.1. SqlQuery

SqlQuery is a reusable, threadsafe class that encapsulates an SQL query. Subclasses
must implement the newRowMapper(..) method to provide a RowMapper instance that can
create one object per row obtained from iterating over the ResultSet that is created
during the execution of the query. The SqlQuery class is rarely used directly because
the MappingSqlQuery subclass provides a much more convenient implementation for
mapping rows to Java classes. Other implementations that extend SqlQuery are
MappingSqlQueryWithParameters and UpdatableSqlQuery.

3.6.2. MappingSqlQuery

MappingSqlQuery is a reusable query in which concrete subclasses must implement the
abstract mapRow(..) method to convert each row of the supplied ResultSet into an
object of the type specified. The following example shows a custom query that maps the
data from the t_actor relation to an instance of the Actor class.

The class extends MappingSqlQuery parameterized with the Actor type. The constructor
for this customer query takes the DataSource as the only parameter. In this
constructor you call the constructor on the superclass with the DataSource and the SQL
that should be executed to retrieve the rows for this query. This SQL will be used to
create a PreparedStatement so it may contain place holders for any parameters to be
passed in during execution.You must declare each parameter using the declareParameter
method passing in an SqlParameter. The SqlParameter takes a name and the JDBC type
as defined in java.sql.Types. After you define all parameters, you call the
compile() method so the statement can be prepared and later executed. This class is
thread-safe after it is compiled, so as long as these instances are created when the DAO
is initialized they can be kept as instance variables and be reused.

The method in this example retrieves the customer with the id that is passed in as the
only parameter. Since we only want one object returned we simply call the convenience
method findObject with the id as parameter. If we had instead a query that returned a
list of objects and took additional parameters then we would use one of the execute
methods that takes an array of parameter values passed in as varargs.

3.6.3. SqlUpdate

The SqlUpdate class encapsulates an SQL update. Like a query, an update object is
reusable, and like all RdbmsOperation classes, an update can have parameters and is
defined in SQL. This class provides a number of update(..) methods analogous to the
execute(..) methods of query objects. The SQLUpdate class is concrete. It can be
subclassed, for example, to add a custom update method, as in the following snippet
where it’s simply called execute. However, you don’t have to subclass the SqlUpdate
class since it can easily be parameterized by setting SQL and declaring parameters.

3.6.4. StoredProcedure

The StoredProcedure class is a superclass for object abstractions of RDBMS stored
procedures. This class is abstract, and its various execute(..) methods have
protected access, preventing use other than through a subclass that offers tighter
typing.

The inherited sql property will be the name of the stored procedure in the RDBMS.

To define a parameter for the StoredProcedure class, you use an SqlParameter or one
of its subclasses. You must specify the parameter name and SQL type in the constructor
like in the following code snippet. The SQL type is specified using the java.sql.Types
constants.

new SqlParameter("in_id", Types.NUMERIC),
new SqlOutParameter("out_first_name", Types.VARCHAR),

The first line with the SqlParameter declares an IN parameter. IN parameters can be
used for both stored procedure calls and for queries using the SqlQuery and its
subclasses covered in the following section.

The second line with the SqlOutParameter declares an out parameter to be used in the
stored procedure call. There is also an SqlInOutParameter for InOut parameters,
parameters that provide an in value to the procedure and that also return a value.

For in parameters, in addition to the name and the SQL type, you can specify a
scale for numeric data or a type name for custom database types. For out parameters
you can provide a RowMapper to handle mapping of rows returned from a REF cursor.
Another option is to specify an SqlReturnType that enables you to define customized
handling of the return values.

Here is an example of a simple DAO that uses a StoredProcedure to call a function,
sysdate(),which comes with any Oracle database. To use the stored procedure
functionality you have to create a class that extends StoredProcedure. In this
example, the StoredProcedure class is an inner class, but if you need to reuse the
StoredProcedure you declare it as a top-level class. This example has no input
parameters, but an output parameter is declared as a date type using the class
SqlOutParameter. The execute() method executes the procedure and extracts the
returned date from the results Map. The results Map has an entry for each declared
output parameter, in this case only one, using the parameter name as the key.

Notice how the overloaded variants of the declareParameter(..) method that have been
used in the TitlesAndGenresStoredProcedure constructor are passed RowMapper
implementation instances; this is a very convenient and powerful way to reuse existing
functionality. The code for the two RowMapper implementations is provided below.

The TitleMapper class maps a ResultSet to a Title domain object for each row in
the supplied ResultSet:

To pass parameters to a stored procedure that has one or more input parameters in its
definition in the RDBMS, you can code a strongly typed execute(..) method that would
delegate to the superclass' untyped execute(Map parameters) method (which has
protected access); for example:

3.7. Common problems with parameter and data value handling

Common problems with parameters and data values exist in the different approaches
provided by the Spring Framework JDBC.

3.7.1. Providing SQL type information for parameters

Usually Spring determines the SQL type of the parameters based on the type of parameter
passed in. It is possible to explicitly provide the SQL type to be used when setting
parameter values. This is sometimes necessary to correctly set NULL values.

You can provide SQL type information in several ways:

Many update and query methods of the JdbcTemplate take an additional parameter in
the form of an int array. This array is used to indicate the SQL type of the
corresponding parameter using constant values from the java.sql.Types class. Provide
one entry for each parameter.

You can use the SqlParameterValue class to wrap the parameter value that needs this
additional information.Create a new instance for each value and pass in the SQL type
and parameter value in the constructor. You can also provide an optional scale
parameter for numeric values.

For methods working with named parameters, use the SqlParameterSource classes
BeanPropertySqlParameterSource or MapSqlParameterSource. They both have methods
for registering the SQL type for any of the named parameter values.

3.7.2. Handling BLOB and CLOB objects

You can store images, other binary data, and large chunks of text in the database. These
large objects are called BLOBs (Binary Large OBject) for binary data and CLOBs (Character
Large OBject) for character data. In Spring you can handle these large objects by using
the JdbcTemplate directly and also when using the higher abstractions provided by RDBMS
Objects and the SimpleJdbc classes. All of these approaches use an implementation of
the LobHandler interface for the actual management of the LOB (Large OBject) data. The
LobHandler provides access to a LobCreator class, through the getLobCreator method,
used for creating new LOB objects to be inserted.

The LobCreator/LobHandler provides the following support for LOB input and output:

BLOB

byte[] — getBlobAsBytes and setBlobAsBytes

InputStream — getBlobAsBinaryStream and setBlobAsBinaryStream

CLOB

String — getClobAsString and setClobAsString

InputStream — getClobAsAsciiStream and setClobAsAsciiStream

Reader — getClobAsCharacterStream and setClobAsCharacterStream

The next example shows how to create and insert a BLOB. Later you will see how to read
it back from the database.

This example uses a JdbcTemplate and an implementation of the
AbstractLobCreatingPreparedStatementCallback. It implements one method,
setValues. This method provides a LobCreator that you use to set the values for the
LOB columns in your SQL insert statement.

For this example we assume that there is a variable, lobHandler, that already is
set to an instance of a DefaultLobHandler. You typically set this value through
dependency injection.

Pass in the lobHandler that in this example is a plain DefaultLobHandler.

2

Using the method setClobAsCharacterStream, pass in the contents of the CLOB.

3

Using the method setBlobAsBinaryStream, pass in the contents of the BLOB.

If you invoke the setBlobAsBinaryStream, setClobAsAsciiStream, or
setClobAsCharacterStream method on the LobCreator returned from
DefaultLobHandler.getLobCreator(), you can optionally specify a negative value for the
contentLength argument. If the specified content length is negative, the
DefaultLobHandler will use the JDBC 4.0 variants of the set-stream methods without a
length parameter; otherwise, it will pass the specified length on to the driver.

Consult the documentation for the JDBC driver in use to verify support for streaming a
LOB without providing the content length.

Now it’s time to read the LOB data from the database. Again, you use a JdbcTemplate
with the same instance variable lobHandler and a reference to a DefaultLobHandler.

3.7.3. Passing in lists of values for IN clause

The SQL standard allows for selecting rows based on an expression that includes a
variable list of values. A typical example would be select * from T_ACTOR where id in
(1, 2, 3). This variable list is not directly supported for prepared statements by the
JDBC standard; you cannot declare a variable number of placeholders. You need a number
of variations with the desired number of placeholders prepared, or you need to generate
the SQL string dynamically once you know how many placeholders are required. The named
parameter support provided in the NamedParameterJdbcTemplate and JdbcTemplate takes
the latter approach. Pass in the values as a java.util.List of primitive objects. This
list will be used to insert the required placeholders and pass in the values during the
statement execution.

Be careful when passing in many values. The JDBC standard does not guarantee that you
can use more than 100 values for an in expression list. Various databases exceed this
number, but they usually have a hard limit for how many values are allowed. Oracle’s
limit is 1000.

In addition to the primitive values in the value list, you can create a java.util.List
of object arrays. This list would support multiple expressions defined for the in
clause such as select * from T_ACTOR where (id, last_name) in ((1, 'Johnson'), (2,
'Harrop'\)). This of course requires that your database supports this syntax.

3.7.4. Handling complex types for stored procedure calls

When you call stored procedures you can sometimes use complex types specific to the
database. To accommodate these types, Spring provides a SqlReturnType for handling
them when they are returned from the stored procedure call and SqlTypeValue when they
are passed in as a parameter to the stored procedure.

Here is an example of returning the value of an Oracle STRUCT object of the user
declared type ITEM_TYPE. The SqlReturnType interface has a single method named
getTypeValue that must be implemented. This interface is used as part of the
declaration of an SqlOutParameter.

You use the SqlTypeValue to pass in the value of a Java object like TestItem into a
stored procedure. The SqlTypeValue interface has a single method named
createTypeValue that you must implement. The active connection is passed in, and you
can use it to create database-specific objects such as StructDescriptors, as shown in
the following example, or ArrayDescriptors.

This SqlTypeValue can now be added to the Map containing the input parameters for the
execute call of the stored procedure.

Another use for the SqlTypeValue is passing in an array of values to an Oracle stored
procedure. Oracle has its own internal ARRAY class that must be used in this case, and
you can use the SqlTypeValue to create an instance of the Oracle ARRAY and populate
it with values from the Java ARRAY.

3.8. Embedded database support

The org.springframework.jdbc.datasource.embedded package provides support for embedded
Java database engines. Support for HSQL,
H2, and Derby is provided
natively. You can also use an extensible API to plug in new embedded database types and
DataSource implementations.

3.8.1. Why use an embedded database?

An embedded database is useful during the development phase of a project because of its
lightweight nature. Benefits include ease of configuration, quick startup time,
testability, and the ability to rapidly evolve SQL during development.

3.8.2. Creating an embedded database using Spring XML

If you want to expose an embedded database instance as a bean in a Spring
ApplicationContext, use the embedded-database tag in the spring-jdbc namespace:

The preceding configuration creates an embedded HSQL database populated with SQL from
schema.sql and test-data.sql resources in the root of the classpath. In addition, as
a best practice, the embedded database will be assigned a uniquely generated name. The
embedded database is made available to the Spring container as a bean of type
javax.sql.DataSource which can then be injected into data access objects as needed.

3.8.3. Creating an embedded database programmatically

The EmbeddedDatabaseBuilder class provides a fluent API for constructing an embedded
database programmatically. Use this when you need to create an embedded database in a
standalone environment or in a standalone integration test like in the following example.

3.8.4. Selecting the embedded database type

Using HSQL

Spring supports HSQL 1.8.0 and above. HSQL is the default embedded database if no type is
specified explicitly. To specify HSQL explicitly, set the type attribute of the
embedded-database tag to HSQL. If you are using the builder API, call the
setType(EmbeddedDatabaseType) method with EmbeddedDatabaseType.HSQL.

Using H2

Spring supports the H2 database as well. To enable H2, set the type attribute of the
embedded-database tag to H2. If you are using the builder API, call the
setType(EmbeddedDatabaseType) method with EmbeddedDatabaseType.H2.

Using Derby

Spring also supports Apache Derby 10.5 and above. To enable Derby, set the type
attribute of the embedded-database tag to DERBY. If you are using the builder API,
call the setType(EmbeddedDatabaseType) method with EmbeddedDatabaseType.DERBY.

3.8.5. Testing data access logic with an embedded database

Embedded databases provide a lightweight way to test data access code. The following is a
data access integration test template that uses an embedded database. Using a template
like this can be useful for one-offs when the embedded database does not need to be
reused across test classes. However, if you wish to create an embedded database that is
shared within a test suite, consider using the Spring TestContext
Framework and configuring the embedded database as a bean in the Spring
ApplicationContext as described in Creating an embedded database using Spring XML and
Creating an embedded database programmatically.

3.8.6. Generating unique names for embedded databases

Development teams often encounter errors with embedded databases if their test suite
inadvertently attempts to recreate additional instances of the same database. This can
happen quite easily if an XML configuration file or @Configuration class is responsible
for creating an embedded database and the corresponding configuration is then reused
across multiple testing scenarios within the same test suite (i.e., within the same JVM
process) –- for example, integration tests against embedded databases whose
ApplicationContext configuration only differs with regard to which bean definition
profiles are active.

The root cause of such errors is the fact that Spring’s EmbeddedDatabaseFactory (used
internally by both the <jdbc:embedded-database> XML namespace element and the
EmbeddedDatabaseBuilder for Java Config) will set the name of the embedded database to
"testdb" if not otherwise specified. For the case of <jdbc:embedded-database>, the
embedded database is typically assigned a name equal to the bean’s id (i.e., often
something like "dataSource"). Thus, subsequent attempts to create an embedded database
will not result in a new database. Instead, the same JDBC connection URL will be reused,
and attempts to create a new embedded database will actually point to an existing
embedded database created from the same configuration.

To address this common issue Spring Framework 4.2 provides support for generating
unique names for embedded databases. To enable the use of generated names, use one of
the following options.

EmbeddedDatabaseFactory.setGenerateUniqueDatabaseName()

EmbeddedDatabaseBuilder.generateUniqueName()

<jdbc:embedded-database generate-name="true" …​ >

3.8.7. Extending the embedded database support

Spring JDBC embedded database support can be extended in two ways:

Implement EmbeddedDatabaseConfigurer to support a new embedded database type.

Implement DataSourceFactory to support a new DataSource implementation, such as a
connection pool to manage embedded database connections.

You are encouraged to contribute back extensions to the Spring community at
jira.spring.io.

3.9. Initializing a DataSource

The org.springframework.jdbc.datasource.init package provides support for initializing
an existing DataSource. The embedded database support provides one option for creating
and initializing a DataSource for an application, but sometimes you need to initialize
an instance running on a server somewhere.

3.9.1. Initializing a database using Spring XML

If you want to initialize a database and you can provide a reference to a DataSource
bean, use the initialize-database tag in the spring-jdbc namespace:

The example above executes the two scripts specified against the database: the first
script creates a schema, and the second populates tables with a test data set. The script
locations can also be patterns with wildcards in the usual ant style used for resources
in Spring (e.g.
classpath*:/com/foo/**/sql/*-data.sql). If a
pattern is used, the scripts are executed in lexical order of their URL or filename.

The default behavior of the database initializer is to unconditionally execute the
scripts provided. This will not always be what you want, for instance, if you are
executing the scripts against a database that already has test data in it. The likelihood
of accidentally deleting data is reduced by following the common pattern (as shown above)
of creating the tables first and then inserting the data — the first step will fail if
the tables already exist.

However, to gain more control over the creation and deletion of existing data, the XML
namespace provides a few additional options. The first is a flag to switch the
initialization on and off. This can be set according to the environment (e.g. to pull a
boolean value from system properties or an environment bean), for example:

The second option to control what happens with existing data is to be more tolerant of
failures. To this end you can control the ability of the initializer to ignore certain
errors in the SQL it executes from the scripts, for example:

In this example we are saying we expect that sometimes the scripts will be executed
against an empty database, and there are some DROP statements in the scripts which
would therefore fail. So failed SQL DROP statements will be ignored, but other failures
will cause an exception. This is useful if your SQL dialect doesn’t support DROP …​ IF
EXISTS (or similar) but you want to unconditionally remove all test data before
re-creating it. In that case the first script is usually a set of DROP statements,
followed by a set of CREATE statements.

The ignore-failures option can be set to NONE (the default), DROPS (ignore failed
drops), or ALL (ignore all failures).

Each statement should be separated by ; or a new line if the ; character is not
present at all in the script. You can control that globally or script by script, for
example:

In this example, the two test-data scripts use @@ as statement separator and only
the db-schema.sql uses ;. This configuration specifies that the default separator
is @@ and override that default for the db-schema script.

If you need more control than you get from the XML namespace, you can simply use the
DataSourceInitializer directly and define it as a component in your application.

Initialization of other components that depend on the database

A large class of applications can just use the database initializer with no further
complications: those that do not use the database until after the Spring context has
started. If your application is not one of those then you might need to read the rest
of this section.

The database initializer depends on a DataSource instance and executes the scripts
provided in its initialization callback (analogous to an init-method in an XML bean
definition, a @PostConstruct method in a component, or the afterPropertiesSet()
method in a component that implements InitializingBean). If other beans depend on the
same data source and also use the data source in an initialization callback, then there
might be a problem because the data has not yet been initialized. A common example of
this is a cache that initializes eagerly and loads data from the database on application
startup.

To get around this issue you have two options: change your cache initialization strategy
to a later phase, or ensure that the database initializer is initialized first.

The first option might be easy if the application is in your control, and not otherwise.
Some suggestions for how to implement this include:

Make the cache initialize lazily on first usage, which improves application startup
time.

Have your cache or a separate component that initializes the cache implement
Lifecycle or SmartLifecycle. When the application context starts up a
SmartLifecycle can be automatically started if its autoStartup flag is set, and a
Lifecycle can be started manually by calling ConfigurableApplicationContext.start()
on the enclosing context.

Use a Spring ApplicationEvent or similar custom observer mechanism to trigger the
cache initialization. ContextRefreshedEvent is always published by the context when
it is ready for use (after all beans have been initialized), so that is often a useful
hook (this is how the SmartLifecycle works by default).

The second option can also be easy. Some suggestions on how to implement this include:

Rely on the default behavior of the Spring BeanFactory, which is that beans are
initialized in registration order. You can easily arrange that by adopting the common
practice of a set of <import/> elements in XML configuration that order your
application modules, and ensure that the database and database initialization are
listed first.

Separate the DataSource and the business components that use it, and control their
startup order by putting them in separate ApplicationContext instances (e.g. the
parent context contains the DataSource, and child context contains the business
components). This structure is common in Spring web applications but can be more
generally applied.

4. Object Relational Mapping (ORM) Data Access

4.1. Introduction to ORM with Spring

The Spring Framework supports integration with the Java Persistence API (JPA) as well
as native Hibernate for resource management, data access object (DAO) implementations,
and transaction strategies. For example, for Hibernate there is first-class support with
several convenient IoC features that address many typical Hibernate integration issues.
You can configure all of the supported features for O/R (object relational) mapping
tools through Dependency Injection. They can participate in Spring’s resource and
transaction management, and they comply with Spring’s generic transaction and DAO
exception hierarchies. The recommended integration style is to code DAOs against plain
Hibernate or JPA APIs.

Spring adds significant enhancements to the ORM layer of your choice when you create
data access applications. You can leverage as much of the integration support as you
wish, and you should compare this integration effort with the cost and risk of building
a similar infrastructure in-house. You can use much of the ORM support as you would a
library, regardless of technology, because everything is designed as a set of reusable
JavaBeans. ORM in a Spring IoC container facilitates configuration and deployment. Thus
most examples in this section show configuration inside a Spring container.

Benefits of using the Spring Framework to create your ORM DAOs include:

Easier testing. Spring’s IoC approach makes it easy to swap the implementations
and configuration locations of Hibernate SessionFactory instances, JDBC DataSource
instances, transaction managers, and mapped object implementations (if needed). This
in turn makes it much easier to test each piece of persistence-related code in
isolation.

Common data access exceptions. Spring can wrap exceptions from your ORM tool,
converting them from proprietary (potentially checked) exceptions to a common runtime
DataAccessException hierarchy. This feature allows you to handle most persistence
exceptions, which are non-recoverable, only in the appropriate layers, without
annoying boilerplate catches, throws, and exception declarations. You can still trap
and handle exceptions as necessary. Remember that JDBC exceptions (including
DB-specific dialects) are also converted to the same hierarchy, meaning that you can
perform some operations with JDBC within a consistent programming model.

General resource management. Spring application contexts can handle the location
and configuration of Hibernate SessionFactory instances, JPA EntityManagerFactory
instances, JDBC DataSource instances, and other related resources. This makes these
values easy to manage and change. Spring offers efficient, easy, and safe handling of
persistence resources. For example, related code that uses Hibernate generally needs to
use the same Hibernate Session to ensure efficiency and proper transaction handling.
Spring makes it easy to create and bind a Session to the current thread transparently,
by exposing a current Session through the Hibernate SessionFactory. Thus Spring
solves many chronic problems of typical Hibernate usage, for any local or JTA
transaction environment.

Integrated transaction management. You can wrap your ORM code with a declarative,
aspect-oriented programming (AOP) style method interceptor either through the
@Transactional annotation or by explicitly configuring the transaction AOP advice in
an XML configuration file. In both cases, transaction semantics and exception handling
(rollback, and so on) are handled for you. As discussed below, in
Resource and transaction management, you can also swap various
transaction managers, without affecting your ORM-related code. For example, you can
swap between local transactions and JTA, with the same full services (such as
declarative transactions) available in both scenarios. Additionally, JDBC-related code
can fully integrate transactionally with the code you use to do ORM. This is useful
for data access that is not suitable for ORM, such as batch processing and BLOB
streaming, which still need to share common transactions with ORM operations.

4.2. General ORM integration considerations

This section highlights considerations that apply to all ORM technologies. The
Hibernate section provides more details and also show these features and
configurations in a concrete context.

The major goal of Spring’s ORM integration is clear application layering, with any data
access and transaction technology, and for loose coupling of application objects. No
more business service dependencies on the data access or transaction strategy, no more
hard-coded resource lookups, no more hard-to-replace singletons, no more custom service
registries. One simple and consistent approach to wiring up application objects, keeping
them as reusable and free from container dependencies as possible. All the individual
data access features are usable on their own but integrate nicely with Spring’s
application context concept, providing XML-based configuration and cross-referencing of
plain JavaBean instances that need not be Spring-aware. In a typical Spring application,
many important objects are JavaBeans: data access templates, data access objects,
transaction managers, business services that use the data access objects and transaction
managers, web view resolvers, web controllers that use the business services,and so on.

4.2.1. Resource and transaction management

Typical business applications are cluttered with repetitive resource management code.
Many projects try to invent their own solutions, sometimes sacrificing proper handling
of failures for programming convenience. Spring advocates simple solutions for proper
resource handling, namely IoC through templating in the case of JDBC and applying AOP
interceptors for the ORM technologies.

The infrastructure provides proper resource handling and appropriate conversion of
specific API exceptions to an unchecked infrastructure exception hierarchy. Spring
introduces a DAO exception hierarchy, applicable to any data access strategy. For direct
JDBC, the JdbcTemplate class mentioned in a previous section provides connection
handling and proper conversion of SQLException to the DataAccessException hierarchy,
including translation of database-specific SQL error codes to meaningful exception
classes. For ORM technologies, see the next section for how to get the same exception
translation benefits.

When it comes to transaction management, the JdbcTemplate class hooks in to the Spring
transaction support and supports both JTA and JDBC transactions, through respective
Spring transaction managers. For the supported ORM technologies Spring offers Hibernate
and JPA support through the Hibernate and JPA transaction managers as well as JTA support.
For details on transaction support, see the Transaction Management chapter.

4.2.2. Exception translation

When you use Hibernate or JPA in a DAO, you must decide how to handle the persistence
technology’s native exception classes. The DAO throws a subclass of a HibernateException
or PersistenceException depending on the technology. These exceptions are all runtime
exceptions and do not have to be declared or caught. You may also have to deal with
IllegalArgumentException and IllegalStateException. This means that callers can only
treat exceptions as generally fatal, unless they want to depend on the persistence
technology’s own exception structure. Catching specific causes such as an optimistic
locking failure is not possible without tying the caller to the implementation strategy.
This trade-off might be acceptable to applications that are strongly ORM-based and/or
do not need any special exception treatment. However, Spring enables exception
translation to be applied transparently through the @Repository annotation:

The postprocessor automatically looks for all exception translators (implementations of
the PersistenceExceptionTranslator interface) and advises all beans marked with the
@Repository annotation so that the discovered translators can intercept and apply the
appropriate translation on the thrown exceptions.

In summary: you can implement DAOs based on the plain persistence technology’s API and
annotations, while still benefiting from Spring-managed transactions, dependency
injection, and transparent exception conversion (if desired) to Spring’s custom
exception hierarchies.

4.3. Hibernate

We will start with a coverage of Hibernate 5 in a Spring
environment, using it to demonstrate the approach that Spring takes towards integrating
O/R mappers. This section will cover many issues in detail and show different variations
of DAO implementations and transaction demarcation. Most of these patterns can be
directly translated to all other supported ORM tools. The following sections in this
chapter will then cover the other ORM technologies, showing briefer examples there.

As of Spring Framework 5.0, Spring requires Hibernate ORM 4.3 or later for JPA support
and even Hibernate ORM 5.0+ for programming against the native Hibernate Session API.
Note that the Hibernate team does not maintain any versions prior to 5.0 anymore and
is likely to focus on 5.2+ exclusively soon.

4.3.1. SessionFactory setup in a Spring container

To avoid tying application objects to hard-coded resource lookups, you can define
resources such as a JDBC DataSource or a Hibernate SessionFactory as beans in the
Spring container. Application objects that need to access resources receive references
to such predefined instances through bean references, as illustrated in the DAO
definition in the next section.

The following excerpt from an XML application context definition shows how to set up a
JDBC DataSource and a Hibernate SessionFactory on top of it:

You can also access a JNDI-located SessionFactory, using Spring’s
JndiObjectFactoryBean / <jee:jndi-lookup> to retrieve and expose it. However, that
is typically not common outside of an EJB context.

4.3.2. Implementing DAOs based on plain Hibernate API

Hibernate has a feature called contextual sessions, wherein Hibernate itself manages
one current Session per transaction. This is roughly equivalent to Spring’s
synchronization of one Hibernate Session per transaction. A corresponding DAO
implementation resembles the following example, based on the plain Hibernate API:

This style is similar to that of the Hibernate reference documentation and examples,
except for holding the SessionFactory in an instance variable. We strongly recommend
such an instance-based setup over the old-school staticHibernateUtil class from
Hibernate’s CaveatEmptor sample application. (In general, do not keep any resources in
static variables unless absolutely necessary.)

The above DAO follows the dependency injection pattern: it fits nicely into a Spring IoC
container, just as it would if coded against Spring’s HibernateTemplate. Of course,
such a DAO can also be set up in plain Java (for example, in unit tests). Simply
instantiate it and call setSessionFactory(..) with the desired factory reference. As a
Spring bean definition, the DAO would resemble the following:

The main advantage of this DAO style is that it depends on Hibernate API only; no import
of any Spring class is required. This is of course appealing from a non-invasiveness
perspective, and will no doubt feel more natural to Hibernate developers.

However, the DAO throws plain HibernateException (which is unchecked, so does not have
to be declared or caught), which means that callers can only treat exceptions as
generally fatal - unless they want to depend on Hibernate’s own exception hierarchy.
Catching specific causes such as an optimistic locking failure is not possible without
tying the caller to the implementation strategy. This trade off might be acceptable to
applications that are strongly Hibernate-based and/or do not need any special exception
treatment.

Fortunately, Spring’s LocalSessionFactoryBean supports Hibernate’s
SessionFactory.getCurrentSession() method for any Spring transaction strategy,
returning the current Spring-managed transactional Session even with
HibernateTransactionManager. Of course, the standard behavior of that method remains
the return of the current Session associated with the ongoing JTA transaction, if any.
This behavior applies regardless of whether you are using Spring’s
JtaTransactionManager, EJB container managed transactions (CMTs), or JTA.

In summary: you can implement DAOs based on the plain Hibernate API, while still being
able to participate in Spring-managed transactions.

4.3.3. Declarative transaction demarcation

We recommend that you use Spring’s declarative transaction support, which enables you to
replace explicit transaction demarcation API calls in your Java code with an AOP
transaction interceptor. This transaction interceptor can be configured in a Spring
container using either Java annotations or XML. This declarative transaction capability
allows you to keep business services free of repetitive transaction demarcation code and
to focus on adding business logic, which is the real value of your application.

4.3.4. Programmatic transaction demarcation

You can demarcate transactions in a higher level of the application, on top of such
lower-level data access services spanning any number of operations. Nor do restrictions
exist on the implementation of the surrounding business service; it just needs a Spring
PlatformTransactionManager. Again, the latter can come from anywhere, but preferably
as a bean reference through a setTransactionManager(..) method, just as the
productDAO should be set by a setProductDao(..) method. The following snippets show
a transaction manager and a business service definition in a Spring application context,
and an example for a business method implementation:

Spring’s TransactionInterceptor allows any checked application exception to be thrown
with the callback code, while TransactionTemplate is restricted to unchecked
exceptions within the callback. TransactionTemplate triggers a rollback in case of an
unchecked application exception, or if the transaction is marked rollback-only by the
application (via TransactionStatus). TransactionInterceptor behaves the same way by
default but allows configurable rollback policies per method.

4.3.5. Transaction management strategies

Both TransactionTemplate and TransactionInterceptor delegate the actual transaction
handling to a PlatformTransactionManager instance, which can be a
HibernateTransactionManager (for a single Hibernate SessionFactory, using a
ThreadLocalSession under the hood) or a JtaTransactionManager (delegating to the
JTA subsystem of the container) for Hibernate applications. You can even use a custom
PlatformTransactionManager implementation. Switching from native Hibernate transaction
management to JTA, such as when facing distributed transaction requirements for certain
deployments of your application, is just a matter of configuration. Simply replace
the Hibernate transaction manager with Spring’s JTA transaction implementation. Both
transaction demarcation and data access code will work without changes, because they
just use the generic transaction management APIs.

For distributed transactions across multiple Hibernate session factories, simply combine
JtaTransactionManager as a transaction strategy with multiple
LocalSessionFactoryBean definitions. Each DAO then gets one specific SessionFactory
reference passed into its corresponding bean property. If all underlying JDBC data
sources are transactional container ones, a business service can demarcate transactions
across any number of DAOs and any number of session factories without special regard, as
long as it is using JtaTransactionManager as the strategy.

Both HibernateTransactionManager and JtaTransactionManager allow for proper
JVM-level cache handling with Hibernate, without container-specific transaction manager
lookup or a JCA connector (if you are not using EJB to initiate transactions).

HibernateTransactionManager can export the Hibernate JDBC Connection to plain JDBC
access code, for a specific DataSource. This capability allows for high-level
transaction demarcation with mixed Hibernate and JDBC data access completely without
JTA, if you are accessing only one database. HibernateTransactionManager automatically
exposes the Hibernate transaction as a JDBC transaction if you have set up the passed-in
SessionFactory with a DataSource through the dataSource property of the
LocalSessionFactoryBean class. Alternatively, you can specify explicitly the
DataSource for which the transactions are supposed to be exposed through the
dataSource property of the HibernateTransactionManager class.

4.3.6. Comparing container-managed and locally defined resources

You can switch between a container-managed JNDI SessionFactory and a locally defined
one, without having to change a single line of application code. Whether to keep
resource definitions in the container or locally within the application is mainly a
matter of the transaction strategy that you use. Compared to a Spring-defined local
SessionFactory, a manually registered JNDI SessionFactory does not provide any
benefits. Deploying a SessionFactory through Hibernate’s JCA connector provides the
added value of participating in the Java EE server’s management infrastructure, but does
not add actual value beyond that.

Spring’s transaction support is not bound to a container. Configured with any strategy
other than JTA, transaction support also works in a stand-alone or test environment.
Especially in the typical case of single-database transactions, Spring’s single-resource
local transaction support is a lightweight and powerful alternative to JTA. When you use
local EJB stateless session beans to drive transactions, you depend both on an EJB
container and JTA, even if you access only a single database, and only use stateless
session beans to provide declarative transactions through container-managed
transactions. Also, direct use of JTA programmatically requires a Java EE environment as
well. JTA does not involve only container dependencies in terms of JTA itself and of
JNDI DataSource instances. For non-Spring, JTA-driven Hibernate transactions, you have
to use the Hibernate JCA connector, or extra Hibernate transaction code with the
TransactionManagerLookup configured for proper JVM-level caching.

Spring-driven transactions can work as well with a locally defined Hibernate
SessionFactory as they do with a local JDBC DataSource if they are accessing a
single database. Thus you only have to use Spring’s JTA transaction strategy when you
have distributed transaction requirements. A JCA connector requires container-specific
deployment steps, and obviously JCA support in the first place. This configuration
requires more work than deploying a simple web application with local resource
definitions and Spring-driven transactions. Also, you often need the Enterprise Edition
of your container if you are using, for example, WebLogic Express, which does not
provide JCA. A Spring application with local resources and transactions spanning one
single database works in any Java EE web container (without JTA, JCA, or EJB) such as
Tomcat, Resin, or even plain Jetty. Additionally, you can easily reuse such a middle
tier in desktop applications or test suites.

All things considered, if you do not use EJBs, stick with local SessionFactory setup
and Spring’s HibernateTransactionManager or JtaTransactionManager. You get all of
the benefits, including proper transactional JVM-level caching and distributed
transactions, without the inconvenience of container deployment. JNDI registration of a
Hibernate SessionFactory through the JCA connector only adds value when used in
conjunction with EJBs.

4.3.7. Spurious application server warnings with Hibernate

In some JTA environments with very strict XADataSource implementations — currently
only some WebLogic Server and WebSphere versions — when Hibernate is configured without
regard to the JTA PlatformTransactionManager object for that environment, it is
possible for spurious warning or exceptions to show up in the application server log.
These warnings or exceptions indicate that the connection being accessed is no longer
valid, or JDBC access is no longer valid, possibly because the transaction is no longer
active. As an example, here is an actual exception from WebLogic:

java.sql.SQLException: The transaction is no longer active - status: 'Committed'. No
further JDBC access is allowed within this transaction.

You resolve this warning by simply making Hibernate aware of the JTA
PlatformTransactionManager instance, to which it will synchronize (along with Spring).
You have two options for doing this:

If in your application context you are already directly obtaining the JTA
PlatformTransactionManager object (presumably from JNDI through
JndiObjectFactoryBean or <jee:jndi-lookup>) and feeding it, for example, to
Spring’s JtaTransactionManager, then the easiest way is to specify a reference to
the bean defining this JTA PlatformTransactionManager instance as the value of the
jtaTransactionManager property for LocalSessionFactoryBean. Spring then makes the
object available to Hibernate.

More likely you do not already have the JTA PlatformTransactionManager instance,
because Spring’s JtaTransactionManager can find it itself. Thus you need to
configure Hibernate to look up JTA PlatformTransactionManager directly. You do this
by configuring an application server- specific TransactionManagerLookup class in the
Hibernate configuration, as described in the Hibernate manual.

The remainder of this section describes the sequence of events that occur with and
without Hibernate’s awareness of the JTA PlatformTransactionManager.

When Hibernate is not configured with any awareness of the JTA
PlatformTransactionManager, the following events occur when a JTA transaction commits:

The JTA transaction commits.

Spring’s JtaTransactionManager is synchronized to the JTA transaction, so it is
called back through an afterCompletion callback by the JTA transaction manager.

Among other activities, this synchronization can trigger a callback by Spring to
Hibernate, through Hibernate’s afterTransactionCompletion callback (used to clear
the Hibernate cache), followed by an explicit close() call on the Hibernate Session,
which causes Hibernate to attempt to close() the JDBC Connection.

In some environments, this Connection.close() call then triggers the warning or
error, as the application server no longer considers the Connection usable at all,
because the transaction has already been committed.

When Hibernate is configured with awareness of the JTA PlatformTransactionManager, the
following events occur when a JTA transaction commits:

the JTA transaction is ready to commit.

Spring’s JtaTransactionManager is synchronized to the JTA transaction, so the
transaction is called back through a beforeCompletion callback by the JTA
transaction manager.

Spring is aware that Hibernate itself is synchronized to the JTA transaction, and
behaves differently than in the previous scenario. Assuming the Hibernate Session
needs to be closed at all, Spring will close it now.

The JTA transaction commits.

Hibernate is synchronized to the JTA transaction, so the transaction is called back
through an afterCompletion callback by the JTA transaction manager, and can
properly clear its cache.

4.4. JPA

The Spring JPA, available under the org.springframework.orm.jpa package, offers
comprehensive support for the
Java Persistence
API in a similar manner to the integration with Hibernate, while being aware of
the underlying implementation in order to provide additional features.

4.4.1. Three options for JPA setup in a Spring environment

The Spring JPA support offers three ways of setting up the JPA EntityManagerFactory
that will be used by the application to obtain an entity manager.

LocalEntityManagerFactoryBean

Only use this option in simple deployment environments such as stand-alone applications
and integration tests.

The LocalEntityManagerFactoryBean creates an EntityManagerFactory suitable for
simple deployment environments where the application uses only JPA for data access. The
factory bean uses the JPA PersistenceProvider autodetection mechanism (according to
JPA’s Java SE bootstrapping) and, in most cases, requires you to specify only the
persistence unit name:

This form of JPA deployment is the simplest and the most limited. You cannot refer to an
existing JDBC DataSource bean definition and no support for global transactions
exists. Furthermore, weaving (byte-code transformation) of persistent classes is
provider-specific, often requiring a specific JVM agent to specified on startup. This
option is sufficient only for stand-alone applications and test environments, for which
the JPA specification is designed.

Obtaining an EntityManagerFactory from JNDI

Use this option when deploying to a Java EE server. Check your server’s documentation
on how to deploy a custom JPA provider into your server, allowing for a different
provider than the server’s default.

Obtaining an EntityManagerFactory from JNDI (for example in a Java EE environment),
is simply a matter of changing the XML configuration:

In such a scenario, the entire persistence unit deployment, including the weaving
(byte-code transformation) of persistent classes, is up to the Java EE server. The JDBC
DataSource is defined through a JNDI location in the META-INF/persistence.xml file;
EntityManager transactions are integrated with the server’s JTA subsystem. Spring merely
uses the obtained EntityManagerFactory, passing it on to application objects through
dependency injection, and managing transactions for the persistence unit, typically
through JtaTransactionManager.

If multiple persistence units are used in the same application, the bean names of such
JNDI-retrieved persistence units should match the persistence unit names that the
application uses to refer to them, for example, in @PersistenceUnit and
@PersistenceContext annotations.

LocalContainerEntityManagerFactoryBean

Use this option for full JPA capabilities in a Spring-based application environment.
This includes web containers such as Tomcat as well as stand-alone applications and
integration tests with sophisticated persistence requirements.

The LocalContainerEntityManagerFactoryBean gives full control over
EntityManagerFactory configuration and is appropriate for environments where
fine-grained customization is required. The LocalContainerEntityManagerFactoryBean
creates a PersistenceUnitInfo instance based on the persistence.xml file, the
supplied dataSourceLookup strategy, and the specified loadTimeWeaver. It is thus
possible to work with custom data sources outside of JNDI and to control the weaving
process. The following example shows a typical bean definition for a
LocalContainerEntityManagerFactoryBean:

The <exclude-unlisted-classes/> shortcut indicates that no scanning for
annotated entity classes is supposed to occur. An explicit 'true' value specified -
<exclude-unlisted-classes>true</exclude-unlisted-classes/> - also means no scan.
<exclude-unlisted-classes>false</exclude-unlisted-classes/> does trigger a scan;
however, it is recommended to simply omit the exclude-unlisted-classes element
if you want entity class scanning to occur.

Using the LocalContainerEntityManagerFactoryBean is the most powerful JPA setup
option, allowing for flexible local configuration within the application. It supports
links to an existing JDBC DataSource, supports both local and global transactions, and
so on. However, it also imposes requirements on the runtime environment, such as the
availability of a weaving-capable class loader if the persistence provider demands
byte-code transformation.

This option may conflict with the built-in JPA capabilities of a Java EE server. In a
full Java EE environment, consider obtaining your EntityManagerFactory from JNDI.
Alternatively, specify a custom persistenceXmlLocation on your
LocalContainerEntityManagerFactoryBean definition, for example,
META-INF/my-persistence.xml, and only include a descriptor with that name in your
application jar files. Because the Java EE server only looks for default
META-INF/persistence.xml files, it ignores such custom persistence units and hence
avoid conflicts with a Spring-driven JPA setup upfront. (This applies to Resin 3.1, for
example.)

When is load-time weaving required?

Not all JPA providers require a JVM agent. Hibernate is an example of one that does not.
If your provider does not require an agent or you have other alternatives, such as
applying enhancements at build time through a custom compiler or an ant task, the
load-time weaver should not be used.

The LoadTimeWeaver interface is a Spring-provided class that allows JPA
ClassTransformer instances to be plugged in a specific manner, depending whether the
environment is a web container or application server. Hooking ClassTransformers
through an
agent
typically is not efficient. The agents work against the entire virtual machine and
inspect every class that is loaded, which is usually undesirable in a production
server environment.

Spring provides a number of LoadTimeWeaver implementations for various environments,
allowing ClassTransformer instances to be applied only per class loader and not
per VM.

Refer to Spring configuration in the AOP chapter for
more insight regarding the LoadTimeWeaver implementations and their setup, either
generic or customized to various platforms (such as Tomcat, WebLogic, GlassFish,
Resin and JBoss).

As described in the aforementioned section, you can configure a context-wide
LoadTimeWeaver using the @EnableLoadTimeWeaving annotation of
context:load-time-weaver XML element. Such a global weaver is picked up by all JPA
LocalContainerEntityManagerFactoryBeans automatically. This is the preferred way of
setting up a load-time weaver, delivering autodetection of the platform (WebLogic,
GlassFish, Tomcat, Resin, JBoss or VM agent) and automatic propagation of the weaver to
all weaver-aware beans:

No matter how the LTW is configured, using this technique, JPA applications relying on
instrumentation can run in the target platform (ex: Tomcat) without needing an agent.
This is important especially when the hosting applications rely on different JPA
implementations because the JPA transformers are applied only at class loader level and
thus are isolated from each other.

Dealing with multiple persistence units

For applications that rely on multiple persistence units locations, stored in various
JARS in the classpath, for example, Spring offers the PersistenceUnitManager to act as
a central repository and to avoid the persistence units discovery process, which can be
expensive. The default implementation allows multiple locations to be specified that are
parsed and later retrieved through the persistence unit name. (By default, the classpath
is searched for META-INF/persistence.xml files.)

<beanid="pum"class="org.springframework.orm.jpa.persistenceunit.DefaultPersistenceUnitManager"><propertyname="persistenceXmlLocations"><list><value>org/springframework/orm/jpa/domain/persistence-multi.xml</value><value>classpath:/my/package/**/custom-persistence.xml</value><value>classpath*:META-INF/persistence.xml</value></list></property><propertyname="dataSources"><map><entrykey="localDataSource"value-ref="local-db"/><entrykey="remoteDataSource"value-ref="remote-db"/></map></property><!-- if no datasource is specified, use this one --><propertyname="defaultDataSource"ref="remoteDataSource"/></bean><beanid="emf"class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean"><propertyname="persistenceUnitManager"ref="pum"/><propertyname="persistenceUnitName"value="myCustomUnit"/></bean>

The default implementation allows customization of the PersistenceUnitInfo instances,
before they are fed to the JPA provider, declaratively through its properties, which
affect all hosted units, or programmatically, through the
PersistenceUnitPostProcessor, which allows persistence unit selection. If no
PersistenceUnitManager is specified, one is created and used internally by
LocalContainerEntityManagerFactoryBean.

4.4.2. Implementing DAOs based on JPA: EntityManagerFactory and EntityManager

Although EntityManagerFactory instances are thread-safe, EntityManager instances are
not. The injected JPA EntityManager behaves like an EntityManager fetched from an
application server’s JNDI environment, as defined by the JPA specification. It delegates
all calls to the current transactional EntityManager, if any; otherwise, it falls back
to a newly created EntityManager per operation, in effect making its usage thread-safe.

It is possible to write code against the plain JPA without any Spring dependencies, by
using an injected EntityManagerFactory or EntityManager. Spring can understand
@PersistenceUnit and @PersistenceContext annotations both at field and method level
if a PersistenceAnnotationBeanPostProcessor is enabled. A plain JPA DAO implementation
using the @PersistenceUnit annotation might look like this:

The DAO above has no dependency on Spring and still fits nicely into a Spring
application context. Moreover, the DAO takes advantage of annotations to require the
injection of the default EntityManagerFactory:

As an alternative to defining a PersistenceAnnotationBeanPostProcessor explicitly,
consider using the Spring context:annotation-config XML element in your application
context configuration. Doing so automatically registers all Spring standard
post-processors for annotation-based configuration, including
CommonAnnotationBeanPostProcessor and so on.

The main problem with such a DAO is that it always creates a new EntityManager through
the factory. You can avoid this by requesting a transactional EntityManager (also
called "shared EntityManager" because it is a shared, thread-safe proxy for the actual
transactional EntityManager) to be injected instead of the factory:

The @PersistenceContext annotation has an optional attribute type, which defaults to
PersistenceContextType.TRANSACTION. This default is what you need to receive a shared
EntityManager proxy. The alternative, PersistenceContextType.EXTENDED, is a completely
different affair: This results in a so-called extended EntityManager, which is not
thread-safe and hence must not be used in a concurrently accessed component such as a
Spring-managed singleton bean. Extended EntityManagers are only supposed to be used in
stateful components that, for example, reside in a session, with the lifecycle of the
EntityManager not tied to a current transaction but rather being completely up to the
application.

Method- and field-level Injection

Annotations that indicate dependency injections (such as @PersistenceUnit and
@PersistenceContext) can be applied on field or methods inside a class, hence the
expressions method-level injection and field-level injection. Field-level
annotations are concise and easier to use while method-level allows for further
processing of the injected dependency. In both cases the member visibility (public,
protected, private) does not matter.

What about class-level annotations?

On the Java EE platform, they are used for dependency declaration and not for resource
injection.

The injected EntityManager is Spring-managed (aware of the ongoing transaction). It is
important to note that even though the new DAO implementation uses method level
injection of an EntityManager instead of an EntityManagerFactory, no change is
required in the application context XML due to annotation usage.

The main advantage of this DAO style is that it only depends on Java Persistence API; no
import of any Spring class is required. Moreover, as the JPA annotations are understood,
the injections are applied automatically by the Spring container. This is appealing from
a non-invasiveness perspective, and might feel more natural to JPA developers.

4.4.3. Spring-driven JPA transactions

You are strongly encouraged to read Declarative transaction management if you have not done
so, to get a more detailed coverage of Spring’s declarative transaction support.

The recommended strategy for JPA is local transactions via JPA’s native transaction
support. Spring’s JpaTransactionManager provides many capabilities known from local
JDBC transactions, such as transaction-specific isolation levels and resource-level
read-only optimizations, against any regular JDBC connection pool (no XA requirement).

Spring JPA also allows a configured JpaTransactionManager to expose a JPA transaction
to JDBC access code that accesses the same DataSource, provided that the registered
JpaDialect supports retrieval of the underlying JDBC Connection. Out of the box,
Spring provides dialects for the EclipseLink and Hibernate JPA implementations.
See the next section for details on the JpaDialect mechanism.

4.4.4. JpaDialect and JpaVendorAdapter

As an advanced feature JpaTransactionManager and subclasses of
AbstractEntityManagerFactoryBean support a custom JpaDialect, to be passed into the
jpaDialect bean property. A JpaDialect implementation can enable some advanced
features supported by Spring, usually in a vendor-specific manner:

This is particularly valuable for special transaction semantics and for advanced
translation of exception. The default implementation used (DefaultJpaDialect) does
not provide any special capabilities and if the above features are required, you have
to specify the appropriate dialect.

As an even broader provider adaptation facility primarily for Spring’s full-featured
LocalContainerEntityManagerFactoryBean setup, JpaVendorAdapter combines the
capabilities of JpaDialect with other provider-specific defaults. Specifying a
HibernateJpaVendorAdapter or EclipseLinkJpaVendorAdapter is the most convenient
way of auto-configuring an EntityManagerFactory setup for Hibernate or EclipseLink,
respectively. Note that those provider adapters are primarily designed for use with
Spring-driven transaction management, i.e. for use with JpaTransactionManager.

See the JpaDialect and JpaVendorAdapter javadocs for more details of its operations
and how they are used within Spring’s JPA support.

4.4.5. Setting up JPA with JTA transaction management

As an alternative to JpaTransactionManager, Spring also allows for multi-resource
transaction coordination via JTA, either in a Java EE environment or with a
standalone transaction coordinator such as Atomikos. Aside from choosing Spring’s
JtaTransactionManager instead of JpaTransactionManager, there are a few further
steps to take:

The underlying JDBC connection pools need to be XA-capable and integrated with
your transaction coordinator. This is usually straightforward in a Java EE environment,
simply exposing a different kind of DataSource via JNDI. Check your application server
documentation for details. Analogously, a standalone transaction coordinator usually
comes with special XA-integrated DataSource implementations; again, check its docs.

The JPA EntityManagerFactory setup needs to be configured for JTA. This is
provider-specific, typically via special properties to be specified as "jpaProperties"
on LocalContainerEntityManagerFactoryBean. In the case of Hibernate, these properties
are even version-specific; please check your Hibernate documentation for details.

Spring’s HibernateJpaVendorAdapter enforces certain Spring-oriented defaults such
as the connection release mode "on-close" which matches Hibernate’s own default in
Hibernate 5.0 but not anymore in 5.1/5.2. For a JTA setup, either do not declare
HibernateJpaVendorAdapter to begin with, or turn off its prepareConnection flag.
Alternatively, set Hibernate 5.2’s "hibernate.connection.handling_mode" property to
"DELAYED_ACQUISITION_AND_RELEASE_AFTER_STATEMENT" to restore Hibernate’s own default.
See Spurious application server warnings with Hibernate for a related note about WebLogic.

Alternatively, consider obtaining the EntityManagerFactory from your application
server itself, i.e. via a JNDI lookup instead of a locally declared
LocalContainerEntityManagerFactoryBean. A server-provided EntityManagerFactory
might require special definitions in your server configuration, making the deployment
less portable, but will be set up for the server’s JTA environment out of the box.

5. Marshalling XML using O/X Mappers

5.1. Introduction

In this chapter, we will describe Spring’s Object/XML Mapping support. Object/XML
Mapping, or O/X mapping for short, is the act of converting an XML document to and from
an object. This conversion process is also known as XML Marshalling, or XML
Serialization. This chapter uses these terms interchangeably.

Within the field of O/X mapping, a marshaller is responsible for serializing an
object (graph) to XML. In similar fashion, an unmarshaller deserializes the XML to
an object graph. This XML can take the form of a DOM document, an input or output
stream, or a SAX handler.

Some of the benefits of using Spring for your O/X mapping needs are:

5.1.1. Ease of configuration

Spring’s bean factory makes it easy to configure marshallers, without needing to
construct JAXB context, JiBX binding factories, etc. The marshallers can be configured
as any other bean in your application context. Additionally, XML namespace-based
configuration is available for a number of marshallers, making the configuration even
simpler.

5.1.2. Consistent interfaces

Spring’s O/X mapping operates through two global interfaces: the Marshaller and
Unmarshaller interface. These abstractions allow you to switch O/X mapping frameworks
with relative ease, with little or no changes required on the classes that do the
marshalling. This approach has the additional benefit of making it possible to do XML
marshalling with a mix-and-match approach (e.g. some marshalling performed using JAXB,
other using Castor) in a non-intrusive fashion, leveraging the strength of each
technology.

5.1.3. Consistent exception hierarchy

Spring provides a conversion from exceptions from the underlying O/X mapping tool to its
own exception hierarchy with the XmlMappingException as the root exception. As can be
expected, these runtime exceptions wrap the original exception so no information is lost.

5.2. Marshaller and Unmarshaller

As stated in the introduction, a marshaller serializes an object to XML, and an
unmarshaller deserializes XML stream to an object. In this section, we will describe
the two Spring interfaces used for this purpose.

5.2.1. Marshaller

Spring abstracts all marshalling operations behind the
org.springframework.oxm.Marshaller interface, the main method of which is shown below.

The Marshaller interface has one main method, which marshals the given object to a
given javax.xml.transform.Result. Result is a tagging interface that basically
represents an XML output abstraction: concrete implementations wrap various XML
representations, as indicated in the table below.

Result implementation

Wraps XML representation

DOMResult

org.w3c.dom.Node

SAXResult

org.xml.sax.ContentHandler

StreamResult

java.io.File, java.io.OutputStream, or java.io.Writer

Although the marshal() method accepts a plain object as its first parameter, most
Marshaller implementations cannot handle arbitrary objects. Instead, an object class
must be mapped in a mapping file, marked with an annotation, registered with the
marshaller, or have a common base class. Refer to the further sections in this chapter
to determine how your O/X technology of choice manages this.

5.2.2. Unmarshaller

Similar to the Marshaller, there is the org.springframework.oxm.Unmarshaller
interface.

This interface also has one method, which reads from the given
javax.xml.transform.Source (an XML input abstraction), and returns the object read. As
with Result, Source is a tagging interface that has three concrete implementations. Each
wraps a different XML representation, as indicated in the table below.

Source implementation

Wraps XML representation

DOMSource

org.w3c.dom.Node

SAXSource

org.xml.sax.InputSource, and org.xml.sax.XMLReader

StreamSource

java.io.File, java.io.InputStream, or java.io.Reader

Even though there are two separate marshalling interfaces ( Marshaller and
Unmarshaller), all implementations found in Spring-WS implement both in one class.
This means that you can wire up one marshaller class and refer to it both as a
marshaller and an unmarshaller in your applicationContext.xml.

5.2.3. XmlMappingException

Spring converts exceptions from the underlying O/X mapping tool to its own exception
hierarchy with the XmlMappingException as the root exception. As can be expected,
these runtime exceptions wrap the original exception so no information will be lost.

Additionally, the MarshallingFailureException and UnmarshallingFailureException
provide a distinction between marshalling and unmarshalling operations, even though the
underlying O/X mapping tool does not do so.

The O/X Mapping exception hierarchy is shown in the following figure:

O/X Mapping exception hierarchy

5.3. Using Marshaller and Unmarshaller

Spring’s OXM can be used for a wide variety of situations. In the following example, we
will use it to marshal the settings of a Spring-managed application as an XML file. We
will use a simple JavaBean to represent the settings:

The application class uses this bean to store its settings. Besides a main method, the
class has two methods: saveSettings() saves the settings bean to a file named
settings.xml, and loadSettings() loads these settings again. A main() method
constructs a Spring application context, and calls these two methods.

This application context uses Castor, but we could have used any of the other marshaller
instances described later in this chapter. Note that Castor does not require any further
configuration by default, so the bean definition is rather simple. Also note that the
CastorMarshaller implements both Marshaller and Unmarshaller, so we can refer to the
castorMarshaller bean in both the marshaller and unmarshaller property of the
application.

This sample application produces the following settings.xml file:

<?xml version="1.0" encoding="UTF-8"?><settingsfoo-enabled="false"/>

5.4. XML configuration namespace

Marshallers could be configured more concisely using tags from the OXM namespace. To
make these tags available, the appropriate schema has to be referenced first in the
preamble of the XML configuration file. Note the 'oxm' related text below:

5.5. JAXB

The JAXB binding compiler translates a W3C XML Schema into one or more Java classes, a
jaxb.properties file, and possibly some resource files. JAXB also offers a way to
generate a schema from annotated Java classes.

Spring supports the JAXB 2.0 API as XML marshalling strategies, following the
Marshaller and Unmarshaller interfaces described in Marshaller and Unmarshaller.
The corresponding integration classes reside in the org.springframework.oxm.jaxb
package.

5.5.1. Jaxb2Marshaller

The Jaxb2Marshaller class implements both the Spring Marshaller and Unmarshaller
interface. It requires a context path to operate, which you can set using the
contextPath property. The context path is a list of colon (:) separated Java package
names that contain schema derived classes. It also offers a classesToBeBound property,
which allows you to set an array of classes to be supported by the marshaller. Schema
validation is performed by specifying one or more schema resource to the bean, like so:

5.6. Castor

Castor XML mapping is an open source XML binding framework. It allows you to transform
the data contained in a java object model into/from an XML document. By default, it does
not require any further configuration, though a mapping file can be used to have more
control over the behavior of Castor.

For more information on Castor, refer to the
Castor web site. The Spring
integration classes reside in the org.springframework.oxm.castor package.

5.6.1. CastorMarshaller

As with JAXB, the CastorMarshaller implements both the Marshaller and Unmarshaller
interface. It can be wired up as follows:

5.6.2. Mapping

Although it is possible to rely on Castor’s default marshalling behavior, it might be
necessary to have more control over it. This can be accomplished using a Castor mapping
file. For more information, refer to Castor
XML Mapping.

The mapping can be set using the mappingLocation resource property, indicated below
with a classpath resource.

The marshaller instance can be configured in two ways, by specifying either the location
of a mapping file (through the mapping-location property), or by identifying Java
POJOs (through the target-class or target-package properties) for which there exist
corresponding XML descriptor classes. The latter way is usually used in conjunction with
XML code generation from XML schemas.

Available attributes are:

Attribute

Description

Required

id

the id of the marshaller

no

encoding

the encoding to use for unmarshalling from XML

no

target-class

a Java class name for a POJO for which an XML class descriptor is available (as
generated through code generation)

no

target-package

a Java package name that identifies a package that contains POJOs and their
corresponding Castor XML descriptor classes (as generated through code generation from
XML schemas)

no

mapping-location

location of a Castor XML mapping file

no

5.7. JiBX

The JiBX framework offers a solution similar to that which Hibernate provides for ORM: a
binding definition defines the rules for how your Java objects are converted to or from
XML. After preparing the binding and compiling the classes, a JiBX binding compiler
enhances the class files, and adds code to handle converting instances of the classes
from or to XML.

For more information on JiBX, refer to the JiBX web
site. The Spring integration classes reside in the org.springframework.oxm.jibx
package.

5.7.1. JibxMarshaller

The JibxMarshaller class implements both the Marshaller and Unmarshaller
interface. To operate, it requires the name of the class to marshal in, which you can
set using the targetClass property. Optionally, you can set the binding name using the
bindingName property. In the next sample, we bind the Flights class:

5.8. XStream

XStream is a simple library to serialize objects to XML and back again. It does not
require any mapping, and generates clean XML.

For more information on XStream, refer to the XStream
web site. The Spring integration classes reside in the
org.springframework.oxm.xstream package.

5.8.1. XStreamMarshaller

The XStreamMarshaller does not require any configuration, and can be configured in an
application context directly. To further customize the XML, you can set analias map,
which consists of string aliases mapped to classes:

By default, XStream allows for arbitrary classes to be unmarshalled, which can lead to
unsafe Java serialization effects. As such, it is not recommended to use the
XStreamMarshaller to unmarshal XML from external sources (i.e. the Web), as this can
result in security vulnerabilities.

If you choose to use the XStreamMarshaller to unmarshal XML from an external source,
set the supportedClasses property on the XStreamMarshaller, like as follows:

This will make sure that only the registered classes are eligible for unmarshalling.

Additionally, you can register
custom
converters to make sure that only your supported classes can be unmarshalled. You might
want to add a CatchAllConverter as the last converter in the list, in addition to
converters that explicitly support the domain classes that should be supported. As a
result, default XStream converters with lower priorities and possible security
vulnerabilities do not get invoked.

Note that XStream is an XML serialization library, not a data binding library.
Therefore, it has limited namespace support. As such, it is rather unsuitable for usage
within Web services.

6. Appendix

6.1. XML Schemas

This part of the appendix lists XML schemas for data access.

6.1.1. The tx schema

The tx tags deal with configuring all of those beans in Spring’s comprehensive support
for transactions. These tags are covered in the chapter entitled
Transaction Management.

You are strongly encouraged to look at the 'spring-tx.xsd' file that ships with the
Spring distribution. This file is (of course), the XML Schema for Spring’s transaction
configuration, and covers all of the various tags in the tx namespace, including
attribute defaults and suchlike. This file is documented inline, and thus the
information is not repeated here in the interests of adhering to the DRY (Don’t Repeat
Yourself) principle.

In the interest of completeness, to use the tags in the tx schema, you need to have
the following preamble at the top of your Spring XML configuration file; the text in the
following snippet references the correct schema so that the tags in the tx namespace
are available to you.

Often when using the tags in the tx namespace you will also be using the tags from the
aop namespace (since the declarative transaction support in Spring is implemented
using AOP). The above XML snippet contains the relevant lines needed to reference the
aop schema so that the tags in the aop namespace are available to you.

To use the tags in the jdbc schema, you need to have the following preamble at the top
of your Spring XML configuration file; the text in the following snippet references the
correct schema so that the tags in the jdbc namespace are available to you.